updated guava lib to ver 15
improved error message in UnknownParamNameProblem
added StreamTester.inputStreamWithContent()/inputStreamToString(), refactored tests
added FileTester.assertContentContains(), added missing tests
added TestFile.assertContentContains()
added DummyOutputClassFile
added OutputClassFile
added InputSourceFile
added ReportingDiagnosticListener
refactored TestSandbox
changed RecursiveFilesIterable to not fail when directory does not exist
added StoredFile.toString()
added FileTester.createContentWithFilePath()