Mac unit

The first commit makes MonoDevelop treat the 'MacUnit' assembly the same as nunit.framework so that the nunit test panel populates with the list of testfixtures/tests.

The second commit modifies the xml output parser slightly so that we cope with the lack of <test-suite type='Namespace' /> elements which the regular desktop runner emits. For our output we need to fake the TestSuiteStarted/Ended events.