api: fix build; regenerate api.txt with fixed signatures

Update to tip (to get 6475062 and 6525047)
Rebuild cmd/api.
Switch to a go1 release branch.
Run go tool api > api/go1.txt.new in release branch.
Back to tip.

R=golang-dev, mikioh.mikioh
CC=golang-dev
https://golang.org/cl/6528047
1 file changed