* Reject import paths of the form cmd/x/y.
* Reject 'go install' of command outside GOPATH
* Clearer error rejecting 'go install' of package outside GOPATH.
* Name temporary binary for first file in 'go run' list or for test.
* Provide a way to pass -ldflags arguments with spaces.
* Pass all Go files (even +build ignored ones) to go fix, go fmt, go vet.
* Reject 'go run foo_test.go'.
* Silence 'exit 1' prints from 'go tool' invocations.
* Make go test -xxxprofile leave binary behind for analysis.
* Reject ~ in GOPATH except on Windows.
* Get a little less confused by symlinks.
* Document that go test x y z runs three test binaries.
* Fix go test -timeout=0.
* Add -tags flag to 'go list'.
* Use pkg/gccgo_$GOOS_$GOARCH for gccgo output.

Fixes #3389.
Fixes #3500.
Fixes #3503.
Fixes #3760.
Fixes #3941.
Fixes #4007.
Fixes #4032.
Fixes #4074.
Fixes #4127.
Fixes #4140.
Fixes #4311.
Fixes #4568.
Fixes #4576.
Fixes #4702.

R=adg
CC=golang-dev
https://golang.org/cl/7225074