codereview: add 'hg undo' command
codereview: add 'hg undo' command

R=adg, r
CC=golang-dev
http://codereview.appspot.com/4423045

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