Grovel physical constants using new CFFI-grovel
Stelian Ionescu has modified CFFI-grovel to generate double-float constants with :type double-float in constant. GSLL has been ported to use that. This requires a version of CFFI which includes the patch of Mon Jun 8 10:29:44 EDT 2009. It works, but until this has a release number, it will stay out of the master GSLL branch.