Treat DistutilsErrors as user errors.

- Added "logical tracebacks" that show functionally what the buildout
  was doing when an error occurs.  Don't show a Python traceback
  unless the -D option is used.

- Added a -D option that causes the buildout to print a traceback and
  start the pdb post-mortem debugger when an error occurs.

be specified in a versions section.

Changed the log format for picked versions.

This will allow a versions feature to be added without updating all
recipes initially.  Later, recipes that support custom versions will
be able to override the defaults by passing options.

- The easy_install module install and build functions now accept a
  versions argument that supplied to mapping from project name to
  version numbers.  This can be used to fix version numbers for
  required distributions and their depenencies.

When a version isn't fixed, using either a versions option or using
  a fixed version number in a requirement, then a debug log message is
  emitted indicating the version picked.  This is useful for setting
  versions options.

- Added a remove testing helper function that removes files or directories.

no longer causes voluminous setuptools output.  Uisng -vv and -vvv
now triggers extra setuptools output.

Improved a logging message.

spurious test failures.  I'm not sure this is really necessary.

```------------
- Added a buildout newest option, to control whether the newest
  distributions should be sought to meet requirements.  This might
  also provide a hint to recipes that don't deal with
  distributions. For example, a recipe that manages subversion
  checkouts might not update a checkout if newest is set to "false".

- The recipe-testing support setUp function now adds the name
  *buildout* to the test namespace with a value that is the path to
  the buildout script in the sample buildout.  This allows tests to
  use

>>> print system(buildout),

rather than:

>>> print system(join('bin', 'buildout')),

Bugs Fixed
```

-------

- Paths returned from update methods replaced lists of installed files
  rather than augmenting them.

Also added a missing tests for upgrading.

allow for getting less than the newest but still getting what's
necessary.

Explicitly specifying a Python executable failed if the output of
running Python with the -V option included a 2-digit (rather than a
3-digit) version number.

Feature Changes
---------------

- By popular demand, added a -o command-line option that is a short
  hand for the assignment buildout:offline=true.

Bugs Fixed
----------

- When deciding whether recipe develop eggs had changed, buildout
  incorrectly considered files in .svn and CVS directories.

Added initialization and arguments options to the scripts recipe.

  easy_install APIs.

- Added an eggs recipe that *just* installes eggs.

- Advertized the scripts recipe for creating scripts.

Updated some tests to deal with the fact that setuptools eggs keep
oscillating between being files and directories.

These are used and tested indirectly in various ways.

----------

- https://bugs.launchpad.net/products/zc.buildout/+bug/71246

Buildout extensions installed as eggs couldn't be loaded in offline
  mode.

----------

- Uninstall recipes weren't loaded correctly in cases where
  no parts in the (new) configuration used the recipe egg.

---------------

- A new command-line argument, -U, suppresses reading user defaults.

- You can now suppress use of an installed-part database
  (e.g. .installed.cfg) by sprifying an empty value for the buildout
  installed option.

depended on were installed too.  This is nice under normal
circumstances, but when the install command is used with a list of
parts, then the promise is that *only* those parts will be installed.
This is an important use case, because it can speed development.

Use the logical size instead.