customize role, race, gender, align choices (trunk only)

Support negation syntax to restrict unwanted race, role, gender, align
options:
        OPTIONS=role:!knight, role:!tourist, race:!orc
prevents them from being picked randomly or
appearing in the pick lists at the start of the game.

include/extern.h

@@ -1802,6 +1802,7 @@ E const char *FDECL(Hello, (struct monst *));
 E const char *NDECL(Goodbye);
 E char *FDECL(build_plselection_prompt, (char *, int, int, int, int, int));
 E char *FDECL(root_plselection_prompt, (char *, int, int, int, int, int));
+E boolean FDECL(setrolefilter, (char *));
 
 /* ### rumors.c ### */