Fix bug #63595 GMP memory management conflicts with other libraries using GMP

Drop use of php memory allocators as this raise various conflicts
with other extensions and libraries which use libgmp.

No other solution found.
We cannot for ensure correct use of allocator with shared lib.

Some memory can allocated before php init
Some memory can be freed after php shutdown

Known broken run cases
- php + curl + gnutls + gmp
- mod_gnutls + mod_php + gnutls + gmp
- php + freetds + gnutls + gmp
- php + odbc + freetds + gnutls + gmp
- php + php-mapi (zarafa) + gnutls + gmp
NEWS
Merge branch 'PHP-5.5' into PHP-5.6

* PHP-5.5:
  NEWS
  Fix bug #63595 GMP memory management conflicts with other libraries using GMP

Conflicts:
	ext/gmp/gmp.c
NEWS
Merge branch 'PHP-5.6'

* PHP-5.6:
  NEWS
  NEWS
  Fix bug #63595 GMP memory management conflicts with other libraries using GMP

Conflicts:
	ext/gmp/gmp.c