
     <li> <code>mpz_init</code> would only store magic values in the
          <code>mpz_t</code> fields, and could be inlined.
     <li> A fixed initializer could even be used by applications, like
          <code>mpz_t z = MPZ_INITIALIZER;</code>, which might be convenient
          for globals.
     </ul>
     The advantages of the current scheme are:
     <ul>
     <li> <code>mpz_set_ui</code> and other similar routines needn't check the
          size allocated and can just store unconditionally.
    