* stringpool.c (set_identifier): New function.
* tree.h: Prototype it.
* c-parse.in: Kill D_YES. If compiled for objc, call
save_and_forget_protocol_qualifiers from init_reswords.
* objc/objc-act.c (remember_protocol_qualifiers,
forget_protocol_qualifiers): Don't diddle C_IS_RESERVED_WORD.
Swap out the non-keyword IDENTIFIER_NODEs for keyword ones, or
vice versa.
(save_and_forget_protocol_qualifiers): New function.
* c-lex.h: Prototype save_and_forget_protocol_qualifiers.