Changes to integer-gmp

Changes to integer-gmp:
commit 01c39638ee8875061c6e388fe62dac63599a0212
Author: Herbert Valerio Riedel <hvr@gnu.org>
Date:   Sun Nov 24 17:53:58 2013 +0100

    Update Autoconf tests for recent GMP version

    This should improve the check for a suitable installed GMP version, to
    implicitly check if GMP provides __gmpz_powm_sec() which has been added
    in GMP version 5.0.0 and switch to the in-tree GMP 5.0.3 source otherwise.

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