These changes adjust the unit tests to compare known values rather than
calculating them on the fly.
The unit test against a 'bad' source has been modified to simply check
for the relevant exception as PHP prevents any output on exceptions
anyway.
The file sample_questions.xml from moodle-stack is properly formed.
The file sample_questions_wrong.xml has mismatching tags.
Comparison is performed with recursive array comparison.
Error messages and returned data structures are compared.
Call with: phpunit lib/tests/xmlize_test.php
