setup and colons in filenames

[Ken Brown]

This is a followup to the thread started here:

   https://cygwin.com/ml/cygwin-patches/2017-q4/msg00012.html

Currently setup's parse_filename is not correctly parsing filenames in 
/etc/setup/installed.db that contain colons, as explained in the above 
thread.  It would be easy to fix this by just ripping out the 'base' 
function, except for the fact that parse_filename is called by 
ScanFindVisitor::visitFile.

I don't know enough about WIN32_FIND_DATA to know whether the call to 
'base' is needed for that use of parse_filename.  If so, is it safe to 
skip all colons in that setting, since we're dealing with Win32 
filenames and they don't see the colons in Cygwin filenames?

Do we need two versions of parse_filename, one that calls base and one 
that doesn't?

Ken