This contains two fixes, that must go along for the tests to pass:

1. Fixed theCollectBasicObject andCollectOnShutdown tests for Mono by fixingMakeAGarbage function to not keep the garbage on the stack during a conservative roots scan (looks like Mono scans some variables, that are already gone).
2. Fixed the crash during runtime shutdown by further simplifyingFinalizer to only store raw pointers to python objects instead of instances ofIPyDisposable and thus replacing Dispose with reliable and simpleDecRef.

This removes some functions fromFinalizer, which previously were public, but should not have been.