     <li> <code>mpz_class(const char *)</code>, etc: since they're normally
          not fast anyway, and we can hide the exception <code>throw</code>.
     <li> <code>mpz_class(string)</code>, etc: to hide the <code>cstr</code>
          needed to get to the C conversion function.
     <li> <code>mpz_class string, char*</code> etc constructors: likewise to
          hide the throws and conversions.
     <li> <code>mpz_class::get_str</code>, etc: to hide the <code>char*</code>
          to <code>string</co