completes the core dependency resolution engine; all we need now is a way
to turn sys.path entries into "distribution sources" that can list
Distribution objects for inclusion in an instance of
AvailableDistributions, and the 'require("SomePkg>=2.7")' API will be
usable.

--HG--
branch : setuptools
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/trunk/setuptools%4041009