Not sure what 1.5 is doing differently, I couldn't find the difference
reading the code but both profiling and timing data show that this
isn't an issue under 1.5/trunk, just under 1.4 into which this change
has already been merged.

git-svn-id: http://svn.zope.org/repos/main/zc.buildout/trunk@124125 62d5b8a3-27da-0310-9561-8e5933582275