Update to mpc-0.9
Prompted by Stathis Kamperis.

Changes:

  * New functions
      + mpc_set_dc, mpc_set_ldc, mpc_get_dc, mpc_get_ldc for
      converting between mpc type variables and C variables of
      type double  _Complex or long double _Complex
      + mpc_sin_cos, computing simultaneously the sine and cosine
  * Speed-ups
      + mpc_pow_si through binary exponentiation
      + mpc_pow_z when the exponent fits in a long
      + mpc_tan through the use of mpc_sin_cos
  * Bug fixes
      + trigonometric functions: infinite loop due to overflow for large arguments
      + exp: close to infinite loop for argument close to 0
      + sqrt: close to infinite loop for argument close to 1
      + add_si: replaced macro by function, since the macro evaluated the same expression twice
  * Logging feature for debugging
    ./configure --enable-logging
    #include "mpc-log.h" instead of #include "mpc.h"
  * Minimally required library versions: gmp 4.3.2, mpfr 2.4.2


(asau)