cmd/vet: continue past first error
Also delete bogus tests for f.pkg (does the file have a package) since all
files have a package attached. The tests for pkg.types and pkg.values
suffice.

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/7418043
syscall: add MSG_FASTOPEN to Linux

Update issue 4842

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/7369060