(scm_is_rational): New.

(scm_is_rational): New.
(scm_i_short2big, scm_i_int2big, scm_i_uint2big, scm_i_size2big,
scm_i_ptrdiff2big, scm_i_long_long2big, scm_i_ulong_long2big):
Removed prototypes.
(scm_make_real, scm_num2dbl, scm_float2num, scm_double2num):
Discouraged by moving to discouraged.h and discouraged.c.
Replaced all uses with scm_from_double.
(scm_num2float, scm_num2double): Discouraged by moving prototype
to discouraged.h and rewriting in terms of scm_to_double.
Replaced all uses with scm_to_double.
(scm_to_double): Do not implement in terms of scm_num2dbl, use
explicit code.
(scm_from_double): Do not implement in terms of scm_make_real, use
explicit code.