Fix ticket:61, using option 2.

src/lisp/gencgc.c:
o Save and restore the FPU state in alloc().

src/compiler/x86/alloc.lisp
src/compiler/x86/array.lisp
src/compiler/x86/call.lisp
src/compiler/x86/float-sse2.lisp
src/compiler/x86/float.lisp
src/compiler/x86/move.lisp
src/compiler/x86/sap.lisp:
o Don't need to use :save-p anymore because the allocation routine
  saves an live registers anyway.  This improves code generation as
  well.

src/general-info/release-20d.txt:
o Update.