largefiles: rearrange how lfconvert detects non-local repos
Mainly this is so we can test that code; it has the side benefit of not
requiring network I/O to reject non-local repo URLs.
$ echo '[Section]' >> $HGRCPATH
$ echo 'KeY = Case Sensitive' >> $HGRCPATH
$ echo 'key = lower case' >> $HGRCPATH
$ hg showconfig Section
Section.KeY=Case Sensitive
Section.key=lower case