Semantic Equality for JUnitReporterTests

Fixes #143.

* Now, both `>` and `&gt;` work for the comparison. (This was the original problem.)
* The expected XML file which was previously a `NSString` literal has been moved out to a file.
* Previously, the time-related attributes were removed using regex on the string representation of the XMLs. This has been changed to use an XPath query.
* The `STAssertEqualObjects()` that previously compared the string output of two string representations of the XMLs have been changed to do a semantic equality comparison.
* Logic for stripping out leading & trailing whitespace as well as removing empty newlines inside <system-out> tags has been added to aid with the semantic equality comparison.