Update to 4.2.4:

Changes between GMP version 4.2.3 and 4.2.4

  Bugs:
  * Fix bug with parsing exponent '+' sign in mpf.
  * Fix an allocation bug in mpf_set_str, also affecting mpf_init_set_str, and
    mpf_inp_str.

  Speedups:
  * None, except that proper processor recognition helps affected processors.

  Features:
  * Recognize new AMD processors.

(wiz)