Changes to integer-gmp

Changes to integer-gmp:
commit ebec3089e10a4a415b0ebf856c827bfbf8726d96
Author: Herbert Valerio Riedel <hvr@gnu.org>
Date:   Sat Jan 4 08:42:01 2014 +0100

    Refactor C-- wrappers to use macros for mpz_t access

    This factors out the recurring task of converting mpz_t structures
    to/from Int#/ByteArrays# pairs and makes the code more readable.

    Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>