modular exponentiation by over 99%. Modified mp_mul and mp_sqr to only
allocate temporary variables when absolutely needed. Changed mp_copy
and mp_init_copy to allocate space according to the amount allocated
in the source, reducing the need to grow the variable later.
git-svn-id: svn://10.0.0.236/trunk@75376 18797224-902f-48f8-a5cc-f745e15eee43
d6a3fe495b