Additional runtime checks.

Patch from http://trac.sagemath.org/ticket/12970 .
In particular, make sure that MPIR builds correctly in VMs
which do not expose all the CPUs capabilities.
remove (u)intmax_t overloads if already defined
Merge remote-tracking branch 'remotes/Jean-Pierre/master'
Upgrade configure.bat and make.bat to work with Visual Studio 2011 / Visual Studio Express 2012, even without yasm.exe
remove YASM build customisation for Visual Studio C only projects
Merge remote-tracking branch 'remotes/Bill/master'
change name of mpz_next_likely_prime to mpz_next_prime_candidate
commit test (no real changes)