Fix register saving on i386
There's a problem on i386 similar to amd64 with regards to register saving and different compiler options. It needs to trick-save ebp and ebx since they cannot be clobbered in some configurations. Example what leads to a crash on Mac OS X 10.7:
CC="/usr/bin/gcc-4.2" LDFLAGS="-Wl,-read_only_relocs,suppress" ARCHFLAGS="-arch i386" CFLAGS="-fomit-frame-pointer -fno-pic" arch -i386 python setup.py test
Stability is more important than speed.