(godoc is excluded from this CL since it will continue to use
/src/pkg in its URL namespace, making the necessary cleanup
more subtle.)
LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/141770043
App Engine needs the whitelist file and it's cleaner if it's
in its own package where it can be imported directly, without
pushing composite.go through a pile of sed.
R=dsymonds, r
CC=golang-dev
https://golang.org/cl/12746045