* throw.c (scm_internal_catch): Make body funcs and handler funcs

* throw.c (scm_internal_catch): Make body funcs and handler funcs
use separate data pointers, to allow them to be designed
independently and reused.
(scm_body_thunk, scm_handle_by_proc, scm_handle_by_message):
Renamed from catch_body, catch_handler, and uncaught_throw; made
generically useful.
(struct scm_catch_body_data): Renamed from catch_body_data; moved
to throw.h.
(scm_catch): Use the above.
(scm_throw): Don't bother printing a message for an uncaught
throw; we establish a default handler in init.
* throw.h (scm_internal_catch): Prototype updated.
(scm_body_thunk, scm_handle_by_proc, scm_handle_by_message): New
decls.
(struct scm_body_thunk_data): New structure, used as data
argument to scm_body_thunk.
* init.c (struct main_func_closure): New structure, packaging up
the data to pass to the user's main function.
(scm_boot_guile): Create one.  Pass it to scm_boot_guile_1.
(scm_boot_guile_1): Pass it through to invoke_main_func.  Use
scm_internal_catch to establish a catch-all handler, using
scm_handle_by_message.  This replaces the special-case code in
scm_throw.
(invoke_main_func): Body function for scm_internal_catch; invoke
the user's main function, using the main_func_closure pointer to
decide what to pass it.
* root.c (struct cwdr_body_data): Remove handler_proc member.
(cwdr): Use scm_handle_by_proc instead of cwdr_handler.
(cwdr_handler): Removed.