Minor fixes and additions to the GMP wrapping.
Minor fixes and additions to the GMP wrapping.

R=rsc
APPROVED=rsc
DELTA=12  (11 added, 0 deleted, 1 changed)
OCL=35715
CL=35715

wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,wesolows/golang-old,wesolows/golang-old,firebitsbr/golang-old,firebitsbr/golang-old,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang-old,firebitsbr/golang-old,wesolows/golang,wesolows/golang