gmpxx on a diet

[Torbjorn Granlund]

Marc Glisse <marc.glisse at inria.fr> writes:

  this patch removes a few hundred lines of code from gmpxx.h without (I
  believe) changing the behaviour at all. (at some point, I should try
  and write a testsuite that counts the number of copies and calls to
  various functions)
  
  It is possible to remove even more code duplication, but then I might
  have to undo it later to add some optimizations, so I stopped at a
  safe point.
  
  Tested with g++-4.4, clang++-2.9 and sunCC-12.2.

Please send change log entries for this change.

-- 
Torbjörn