unsafe: add missing case to doc for Pointer
unsafe: add missing case to doc for Pointer

Fixes issue 1433.

R=r, gri
CC=golang-dev
http://codereview.appspot.com/3999047
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go