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

  path and a flag indicating whether the downloaded copy is a temporary file
- use this flag to clean up temporary files both when downloading extended
  configuration files and in the tests

Conflicts:
	CHANGES.txt
	src/zc/buildout/buildout.py

  could be inserted into sys.path if a relative path was used to run
  the generated script.

Also fixed some spurious failures in the bootstrap test.

fixed test, so it does not break when using python 2.6 (previously a deprecation warning was displayed there inside the test output)

``zc.buildout.testing.buildoutSetUp`` installs a new handler in the python root logging facility. This handler is now removed during tear down as it might disturb other packages reusing buildout's testing infrastructure.

On Mac OS X the path returned by tempfile.mkdtemp is not the real path.
This makes the realtive_path test of easy_install.txt failing.
Calling os.path.realpath on the base directory fixed this testfailure for python 2.4 - 2.6.