largefiles: fix _always for match overrides
Upcoming patches will speed dirstate.walk up by not filtering based on the
match function when match.always() is True. For that to work, match.always()
needs to be accurate. Previously it wasn't so for largefiles.
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$ hg init
$ echo '[Section]' >> $HGRCPATH
$ echo 'KeY = Case Sensitive' >> $HGRCPATH
$ echo 'key = lower case' >> $HGRCPATH
$ hg showconfig Section
Section.KeY=Case Sensitive
Section.key=lower case