r=ftang, sr=blizzard, a= asa@mozilla.org for checkin to the trunk.
add pref to control this new code
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this is a 'better' redo of bug 4760:
re-enable special chars (eg: smart quotes) in double byte fonts
but put in a special transliterator so single byte docs do not
use the large special chars from double byte fonts
side benefit: the font lang group search code allows us to get most of
special chars from single byte fonts (eg: iso-8859-15)
git-svn-id: svn://10.0.0.236/trunk@97473 18797224-902f-48f8-a5cc-f745e15eee43
012d87b0b1