NOTE: This patch has been committed. OK, I decided to figure out why cperl was so god-damn slow with font-locking enabled. This addresses that and (big surprise) some more syntax cache bugs discovered along the way. 1. the updating of mirror tables every time a syntax table was modified was taking up huge amounts of time so i added a dirty flag and made the updating "just-in-time". 2. no-longer-used char-table-entries were not getting "freed", generating tons of garbage. 3. syntax_match() was being incorrectly called on mirror tables in the cache, not the original syntax table. now -- which of these go into 21.4? #3 obviously. what about 1 and 2? they make a huge difference in cperl but are not strictly bug fixes. ben