cgo: rename internal f to avoid conflict with possible C global named f
cgo: rename internal f to avoid conflict with possible C global named f

Fixes issue 1452.

R=r
CC=golang-dev
http://codereview.appspot.com/4023060
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go