h pointers to <code>mpz_add</code> etc, which doesn't work
     when those routines are coming from a DLL (because they're effectively
     function pointer global variables themselves).  Need to rearrange perhaps
     to a set of calls to a test function rather than iterating over an array.
<li> <code>mpz_pow_ui</code>: Detect when the result would be more memory than
     a <code>size_t</code> can represent and raise some suitable exception,
     probably an alloc call asking for <code>SIZE_T_MAX</code>, 