flag: fix error in documentation example. Fixes issue 1615. This time for sure.
flag: fix error in documentation example.
Fixes issue 1615.
This time for sure.

R=rsc, gri
CC=golang-dev
http://codereview.appspot.com/4275079

tav/go,tav/go,tav/go,tav/go,tav/go,tav/go,tav/go