What I've done to fix this:
- add a sclang-class-list variable in sclang-language.el, which is a
list of all the classes known to sclang. this is populated when
sclang starts.
- update sclang-font-lock-class-keyword-matcher in
sclang-mode.el. since the sclang-class-name-regexp now will match
all words that start with a capital letter (see next bullet point
for that change), this function had to be updated to check to make
sure that the word starting with a capital letter is in the list of
classes. if it is, then we know it's a class and it gets
highlighted. if it's not, then it's just something the user typed
with a capital letter, so we don't highlight it.
- update sclang-update-font-lock in sclang-mode.el. instead of
generating a huge regexp from a list of all the classes in
SuperCollider, just run the normal fontification from that
function. this avoids making the regexp too big and thus prevents
fontification from failing.