Hello rsc (cc: golang-dev@googlegroups.com), I'd like you to review this change.
LGTM
*** Submitted as http://code.google.com/p/go/source/detail?r=3c304a2dbfbc *** handle nils safely in Printf. add some tests for erroneous formats. R=rsc CC=golang-dev http://codereview.appspot.com/201058