TestParenting01dAWT: Add waitForVisible after toggling NEWT child window visibility helping robostness of test case.
Bug 938 - MemoryObject.java has no more equals() method

Re-adding 'equals(..)' method erroneously removed with commit 8457bf35fee253d9af29ff1150a9671f6896fc17.

'equals(..)' is important to allow the HashMap<> for glMapBuffer(..) work properly!
Bug 942 - Share GLBufferStateTracker ; Unify GLBufferStateTracker and GLBufferSizeTracker (simplification)

Due to future mapped buffer tracking, the GLBufferStateTracker instance shall be shared
across shared GLContextImpl instances similar to GLSizeStateTracker!

This allows us to merge GLSizeStateTracker code into GLBufferStateTracker
to simplify the implementation.

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Clear the GLBufferStateTracker (@destruction) only if no more
created shares are left!

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