gc: more accurate description of -w and -W switches.
gc: more accurate description of -w and -W switches.

The -w switch actually prints steps of the syntax tree walks
while -W prints a summary before and after the walk.

R=golang-dev, rsc
CC=golang-dev, remy
http://codereview.appspot.com/5444049

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

dsriram/golang,gnanderson/go,tv42/old-go,apparentlymart/golang,gnanderson/go,dsriram/golang,gnanderson/go,tv42/old-go,tv42/old-go,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,gnanderson/go,apparentlymart/golang,gnanderson/go,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,dsriram/golang,dsriram/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,dsriram/golang,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,dsriram/golang,gnanderson/go,tv42/old-go