tommath.h contains declarations for the public part of the library.
tommath_private.h contains the functions which are private to ltm and
should not be exposed to the public.
The implementation of the expt_d functionality is now implemented in the
mp_expt_d_ex() function.
The user can now choose between the old (more timing resistant) version
and the new version by modification of the parameter 'fast'.
mp_expt_d() defaults to the old version
