Add FcMatchScan to resolve Delicious font matching issues (bug #6769)

Add FcMatchScan to resolve Delicious font matching issues (bug #6769)

The Delicious family includes one named Delicious Heavy, a bold variant
which is unfortunately marked as having normal weight. Because the family
name is 'Delicious', fontconfig accidentally selects this font instead of
the normal weight variant. The fix here rewrites the scanned data by running
the scanned pattern through a new substitution sequence tagged with
<match target=scan>; a sample for the Delicious family is included to
demonstrate how it works (and fix Delicious at the same time).

Also added was a new match predicate -- the 'decorative' predicate which is
automatically detected in fonts by searching style names for key decorative
phrases like SmallCaps, Shadow, Embosed and Antiqua. Suggestions for
additional decorative key words are welcome. This should have little effect
on font matching except when two fonts share the same characteristics except
for this value.