Revert to old style path.

- Incrementing didn't work properly when extending multiple files.
  https://bugs.launchpad.net/zc.buildout/+bug/421022

windows, urllib raises an invalid ioerror.

windows, urllib raises an invalid ioerror.

  The standard Python -m option didn't work for custom interpreters.

  Scripts run using generated interpreters didn't have __file__ set correctly.

  Scripts generated with relative-paths eanbled couldn't be
  symbolocally linked to other locations and still work.

  Option incrementing and decrementing didn't work for options
  specified on the command line.

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(Also stop writing doc.txt. --long-description is better. And
rearranged setup.py a little.)

- When doing variable substitutions, you can omit the section name to
  refer to a variable in the same section (e.g. ${:foo}).

- When doing variable substitution, you can use the special option,
  ``_buildout_section_name_`` to get the section name.  This is most handy
  for getting the current section name (e.g. ${:_buildout_section_name_}).

- A new special option, ``<`` allows sections to be used as macros.

refer to a variable in the same section (e.g. ${:foo}).

When doing variable substitution, you can use the special option,
``_buildout_section_name_`` to get the section name.  This is most handy
for getting the current section name (e.g. ${:_buildout_section_name_}.

(Also removed some extra imports and made formatting changes.)

does it for easy-install:

- require the download cache (but not namespace directories) to be an
  existing directory in order to catch configuration bugs

- made relative download cache paths refer to the buildout directory