ref: https://bugs.launchpad.net/bugs/149352

  existing buildouts.  Use::

[buildout]
    prefer-final = true

to get the new policy.  The new policy will go into effect in
  buildout 2.

  both final and non-final versions satisfy a requirement, then the
  final version will be used even if it is older.  The normal way to
  override this for specific packages is to specifically require a
  non-final version, either specifically or via a lower bound.

- There is a buildout prefer-final version that can be used with a
  value of "false"::

prefer-final = false

To prefer newer versions, regardless of whether or not they are
  final, buildout-wide.

to work with recent change changes to use expanduser rather than
reading $HOME directly.

for versions if the given requirement had an upper limit and we
already had the distribution whos version was the upper limit.

Added simpler tested code that checks for the simpler case that teh
requirement is for a specific version and we already have that
version.  In general, specifying upper limits other than a single
version is kind of dumb, so it's not worth optimizing for that case.

Also rearranged some code to work with emacs python mode. :)

deterministic output by outputing all of standard output followed
by all of standard error.

Removed a test that was obsoleted by a setuptools improvement in
handling failed downloads.

Updated to reflect a change in bootstrapping. (I wonder why this
wasn't needed sooner.)

zc.buildout logger.  This reduces noise in the output.  This change
was so far reaching, I decided to go ahead and clean up lots of log
messages, adding some missing periods and adding quotes around
requirement strings and file paths.

in easy_install.py, added logging to show why distributions are added
in verbose mode and removed recusive code to show requirement chains
when errors occurred.

  an empty configuration file and then bootstraps.

- Except when using the new init command, it is now an error to run
  buildout without a configuration file.

- 75607: buildout should not run if it creates an empty buildout.cfg

setuptools requires that file urls that point to directories must
end in a "/".  Added a workaround.

  install and update methods.

- 59270: Buggy recipes can cause failures in later recipes via chdir

Also updated a test to reflect logging of script installation.

api to help clean up created paths when errors occir in recipe install
and update methods.

Made sure buildout exited with a non-zeo exit status when errors
occurred.

https://bugs.launchpad.net/zc.buildout/+bug/71353