go/misc/dist: Keep file modes when copying.
go/misc/dist: Keep file modes when copying.

R=adg
CC=golang-dev
https://codereview.appspot.com/7221055

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