GMP kernel activated by default when available

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

Hello PARI-lovers,

I have made a change to PARI2.4.3SVN (r11717):
The GMP kernel is now chosen by default when GMP is available,
because the GMP kernel is much faster than the traditional PARI
kernel.

This will only affect you if you have built PARI without GMP. In that
case, if you want to continue to use PARI without GMP, you need to
pass --without-gmp to Configure.

The only downside is that binaries build for PARI-without-gmp will not
work with PARI-with-gmp, so you will need to rebuild them. 

Cheers,
Bill.