strings.Split: make the default to split all.

Change the signature of Split to have no count,
assuming a full split, and rename the existing
Split with a count to SplitN.
Do the same to package bytes.
Add a gofix module.

R=adg, dsymonds, alex.brainman, rsc
CC=golang-dev
https://golang.org/cl/4661051

src/cmd/cgo/out.go

@@ -148,7 +148,7 @@ func dynimport(obj string) {
 			fatalf("cannot load imported symbols from PE file %s: %v", obj, err)
 		}
 		for _, s := range sym {
-			ss := strings.Split(s, ":", -1)
+			ss := strings.Split(s, ":")
 			fmt.Printf("#pragma dynimport %s %s %q\n", ss[0], ss[0], strings.ToLower(ss[1]))
 		}
 		return