* defs.h (enum return_reason): Renumber so that all values are

* defs.h (enum return_reason): Renumber so that all values are
negative.
(RETURN_MASK): Negate reason.
(catch_exception_ftype): Declare.
(catch_exceptions): Declare.
* top.c (catcher): New function, based on catch_errors.  Add in
parameter func_uiout and out parameters func_val, func_caught and
func_cleanup.  Change type of func to catch_exceptions_ftype.
Save/restore uiout.
(struct catch_errors_args): Define.
(do_catch_errors): New function.
(catch_errors): Rewrite, use do_catch_errors and catcher.
(catch_exceptions): New function, use catcher.