PHPUnit test suite fails on Windows

PHPUnit's own test suite has various failures on Windows currently.  There are two dominant causes:

1. `DIRECTORY_SEPARATOR` mismatches in PHPT tests.
1. Expected stack traces in PHPT tests do not account for an additional stack frame that is caused by `PHPUnit_Util_PHP_Windows::process()`.

Lastly, there's a difference in libxml behavior with regard to `PHPUnit_Util_XML::load()` on Windows, which causes configuration.xml tests to fail, because relative file paths are not resolved correctly - they're resolved base on the current working directory, instead of the directory in which the configuration file is contained; setting `DOMDocument::$documentURI` does not help in any way (but is required and MUST be set before loading the XML for XInclude to work).

Hard to say what the likelihood of a clash would be without some sort of empirical data. If we really believe it's an issue, we could always add an interface for supplying the exact filenames to blacklist.