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.


git-svn-id: http://svn.zope.org/repos/main/zc.buildout/trunk@72071 62d5b8a3-27da-0310-9561-8e5933582275