Fix: AttributeError: 'module' object has no attribute 'HAVE_DECL_MPZ_POWM_SEC'

Fixing run time error caused by invalid attribute reference on object:

from Crypto import Random
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/__init__.py", line 29, in <module>
    from Crypto.Random import _UserFriendlyRNG
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/_UserFriendlyRNG.py", line 38, in <module>
    from Crypto.Random.Fortuna import FortunaAccumulator
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/Fortuna/FortunaAccumulator.py", line 39, in <module>
    import FortunaGenerator
  File "/usr/lib64/python2.6/site-packages/Crypto/Random/Fortuna/FortunaGenerator.py", line 34, in <module>
    from Crypto.Util.number import ceil_shift, exact_log2, exact_div
  File "/usr/lib64/python2.6/site-packages/Crypto/Util/number.py", line 56, in <module>
    if _fastmath is not None and not getattr(_fastmath, "HAVE_DECL_MPZ_POWM_SEC"):
AttributeError: 'module' object has no attribute 'HAVE_DECL_MPZ_POWM_SEC'