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/pkg/runtime/debug/stack.go

@@ -52,7 +52,7 @@ func stack() []byte {
 			if err != nil {
 				continue
 			}
-			lines = bytes.Split(data, []byte{'\n'}, -1)
+			lines = bytes.Split(data, []byte{'\n'})
 			lastFile = file
 		}
 		line-- // in stack trace, lines are 1-indexed but our array is 0-indexed