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.


git-svn-id: http://svn.zope.org/repos/main/zc.buildout/trunk@77454 62d5b8a3-27da-0310-9561-8e5933582275