- Do not use a property for a local variable.
- Use new-style class.
- Stop using logger.
- Save a few getattr calls.
- Do not keep references to buildout & options outside of __init__ .
- Convert mode in __init__ to detect errors early.
- Factorise several accesses (buildout['buildout'], properties)
- Drop redundant "cache" download.Download parameter: it is automatically
  fetched from first parameter internally.
- "Backward compatibility with other recipes" is just not "backward".
- Return downloaded file path, not just the optionally-created directory.

Squashed commit of the following:

commit 275d6e01
Merge: 42342905 319c7223
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Thu Sep 8 15:20:10 2011 +0200

    Merge branch 'master' into suggested-improvements

    Conflicts:
    	slapos/recipe/build.py

commit 42342905
Author: Antoine Catton <acatton@tiolive.com>
Date:   Thu Sep 8 15:12:11 2011 +0200

    Minor: use shlex to parse patch options

commit 7994dcc8
Author: Antoine Catton <acatton@tiolive.com>
Date:   Thu Sep 8 15:11:21 2011 +0200

    Buxfix: the patch wasn't send in stdin

commit ee8f3249
Author: Antoine Catton <acatton@tiolive.com>
Date:   Thu Sep 8 12:04:22 2011 +0200

    Use shlex to split command line

Squashed commit of the following:

commit 506d815ff7e1d7b7b5b3c5edcfcea744c5b2201e
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:54:59 2011 +0200

    Support multiline values.

commit c5d9415000fb072a07164bbdd5c276e53470b265
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:48:54 2011 +0200

    Fix compatibility layer.

commit 1e301c7ba51060d944fea9ff2be1aba00e3a48b6
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:41:41 2011 +0200

    Go back to development.

commit 9f523c49
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:40:00 2011 +0200

    Prepare 0.5 release.

commit fcaf5c04
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:39:28 2011 +0200

    Be more compatible.

commit 5284491f
Merge: 2d7dc0b3 f15bb155
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:28:40 2011 +0200

    Merge branch 'master' into cmmi

commit 2d7dc0b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:22:13 2011 +0200

    Explain more about patches.

commit d5df4cdc
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:18:55 2011 +0200

    Provide better looking patches.

commit c6befb05
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:15:32 2011 +0200

    Support make-command and make-options.

    Fix configure-command.

commit d2212cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:04:05 2011 +0200

    Allow to override configure command.

commit 4321b38a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:49 2011 +0200

    Share applyPatchList with in base class.

commit 4a2ea3b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:29 2011 +0200

    Support no md5sum.

commit 2cd36cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:16 2011 +0200

    Show how to patch.

commit 8cd9ea9c
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:53:45 2011 +0200

    Allow options per patch.

commit 84fea623
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:48:47 2011 +0200

    Allow patching.

commit 8934eb92
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:30:46 2011 +0200

    Allow to keep directories in case of error.

    Default is to remove.

commit 74d0b2bd
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:24:49 2011 +0200

    Allow to have a=b=c, where a is key and b=c is value.

commit 034c2381
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:17:07 2011 +0200

    Another typo.

commit f5abcde0
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:15:44 2011 +0200

    Follow fixed typo.

commit 5b950e26
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:35 2011 +0200

    Extract does not need md5sum.

commit 6f725632
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:14 2011 +0200

    Pass md5sum directly.

commit 9f42d22a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:53 2011 +0200

    Allow to pass empty md5sum.

commit c91fafb1
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:15 2011 +0200

    Fix typos.

commit 8919378d
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:12:31 2011 +0200

    Fix examples.

Squashed commit of the following:

commit 2d7dc0b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:22:13 2011 +0200

    Explain more about patches.

commit d5df4cdc
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:18:55 2011 +0200

    Provide better looking patches.

commit c6befb05
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:15:32 2011 +0200

    Support make-command and make-options.

    Fix configure-command.

commit d2212cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 17:04:05 2011 +0200

    Allow to override configure command.

commit 4321b38a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:49 2011 +0200

    Share applyPatchList with in base class.

commit 4a2ea3b3
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:29 2011 +0200

    Support no md5sum.

commit 2cd36cb7
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:56:16 2011 +0200

    Show how to patch.

commit 8cd9ea9c
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:53:45 2011 +0200

    Allow options per patch.

commit 84fea623
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:48:47 2011 +0200

    Allow patching.

commit 8934eb92
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:30:46 2011 +0200

    Allow to keep directories in case of error.

    Default is to remove.

commit 74d0b2bd
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:24:49 2011 +0200

    Allow to have a=b=c, where a is key and b=c is value.

commit 034c2381
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:17:07 2011 +0200

    Another typo.

commit f5abcde0
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:15:44 2011 +0200

    Follow fixed typo.

commit 5b950e26
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:35 2011 +0200

    Extract does not need md5sum.

commit 6f725632
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:14:14 2011 +0200

    Pass md5sum directly.

commit 9f42d22a
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:53 2011 +0200

    Allow to pass empty md5sum.

commit c91fafb1
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:13:15 2011 +0200

    Fix typos.

commit 8919378d
Author: Łukasz Nowak <luke@nexedi.com>
Date:   Tue Sep 6 16:12:31 2011 +0200

    Fix examples.

slapos.cookbook provided it before, but it is simple functionality, which does
not need so many dependencies.

Additionaly support slapos_update_promise

pipeCommand allows to simulate shell pipes.

failIfPathExists allows to stop in case of path which exists.

Read md5sum passed to method directly.