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).

> `strpos($file, sys_get_temp_dir() . '\\PHPUnit') === 0`

To quote the [PHP manual](http://php.net/manual/en/function.tempnam.php#refsect1-function.tempnam-parameters):
> **Note:** Windows uses only the first three characters of prefix.

The temporary file names are still compatible with filesystems that only support [8.3 filenames](http://en.wikipedia.org/wiki/8.3_filename).

We can minimally adjust it and append `'PHP'` to the blacklisted pathname (which are checked via `strpos()` anyway), although the likelihood of a prefix-clash would be relatively high, because `'PHP'` is a fairly generic prefix for PHP software. :wink: 

But yeah, let me do that, so as to do the maximum to avoid false-positives.