* debug.c, unif.c: use scm_out_of_range instead of

* debug.c, unif.c: use scm_out_of_range instead of
wta for range errors (ASSERT still needs work).

* error.c, error.h (scm_out_of_range): new procedure.

* error.c, error.h (scm_out_of_range_key): new key.

* posix.c (scm_sync): #else was missing.

* error.c, error.h: append _key to names scm_num_overflow and
scm_system_error.

* __scm.h (SCM_SYSMISSING, SCM_NUM_OVERFLOW): use SCM_BOOL_F instead
of consing an empty list.
(SCM_SYSERROR etc.): move into error.c, make them procedures instead
of macros, saves code and string space.
error.c, fports.c, numbers.c, posix.c, ioext.c, filesys.c, socket.c,
fdsocket.c, simpos.c: change names of SCM_SYSERROR etc., to
lower case.  Rename scm_syserror_m to scm_syserror_msg.
error.h: prototypes for new procedures.