Fix #725: Escape newlines in test output messages

Tested by renaming a test:

```Diff
diff --git a/test/src/test/scala/scala/scalajs/test/compiler/BooleanTest.scala b/test/src/test/scala/scala/scalajs/test/compiler/BooleanTest.scala
index 9756237..7a72c23 100644
--- a/test/src/test/scala/scala/scalajs/test/compiler/BooleanTest.scala
+++ b/test/src/test/scala/scala/scalajs/test/compiler/BooleanTest.scala
@@ -15,7 +15,7 @@ object BooleanTest extends JasmineTest {
 
   describe("Boolean primitives") {
 
-    it("&, | and ^ on booleans should return booleans") {
+    it("&, | and ^ on booleans \\should \r\n\n\n\r\n \\\\return booleans") {
       expect(js.typeOf(true & false)).toEqual("boolean")
       expect(js.typeOf(true | false)).toEqual("boolean")
       expect(js.typeOf(true ^ false)).toEqual("boolean")
```