Fix tests on windows

Attempt to build 'metadata' on Windows platform fails while running 'org.jboss.metadata.ejb.test.extension.ExtensionTestCase'. The root cause of the problem is using of System.getProperty("user.dir") statement to construct part of URL for test schema file - on Windows this results in incorrect URL due to different path separators. Another problem occurs if non-ASCII characters are present in the patch - they need to be properly encoded.