cmd/go: do not ignore DepsErrors in 'go run'

Fixes #3490.

R=golang-dev, dave, rsc
CC=golang-dev
https://golang.org/cl/6040046

src/cmd/go/run.go

@@ -49,6 +49,10 @@ func runRun(cmd *Command, args []string) {
 	if p.Error != nil {
 		fatalf("%s", p.Error)
 	}
+	for _, err := range p.DepsErrors {
+		errorf("%s", err)
+	}
+	exitIfErrors()
 	if p.Name != "main" {
 		fatalf("go run: cannot run non-main package")
 	}