(setup_lookup_flags): The last argument changed

(setup_lookup_flags): The last argument changed
to lookup_flags.  Just set the elements to 1 or 0.
(gstring_insert_for_gpos): New function.
(lookup_gpos): New arg accumulate.  Insert pseudo glyphs to
accumulate positioning if necessary.
(OTF_drive_gsub_internal): Adjusted for the change of
setup_lookup_flags.
(OTF_drive_gpos_internal): Renamed from OTF_drive_gpos.  Adjusted
for the change of setup_lookup_flags and lookup_gpos.
(OTF_drive_gpos): Just call OTF_drive_gpos_internal with
accumulate == 0.
(OTF_drive_gpos2): New function.