``to_filename()`` function that escapes project names and versions for
safe use in constructing egg filenames from a Distribution object's
metadata.

Note that allowing dots may now cause problems for projects with '.' in
the name that were previously installed, since such projects had to be
spelled with a '-' before.  The '-' name will no longer match the '.'
project, and there is no real room for backward compatibility here.  :(

--HG--
branch : setuptools
extra : convert_revision : svn%3A6015fed2-1504-0410-9fe1-9d1591cc4771/sandbox/trunk/setuptools%4041994