match: consider filesets as "anypats"
Matt suggested this on IRC, I do not think the choice is obvious, but this one
makes things simpler because while filesets are turned into a list of files
into the match objects, it would more be difficult to tell invalid files passed
in pats from those expanded from filesets.
$ echo '[Section]' >> $HGRCPATH
$ echo 'KeY = Case Sensitive' >> $HGRCPATH
$ echo 'key = lower case' >> $HGRCPATH
$ hg showconfig Section
Section.KeY=Case Sensitive
Section.key=lower case