Warning Fixes for Windows and Unix

This cleans up a bunch of Windows and Linux warnings. Maybe we should switch our Xcode options to be more strict as well?

The remaining warnings are in:
* PositionalAudioRingBuffer.cpp - a signed/unsigned compare
* AttributeRegistry.h - several " dereferencing type-punned pointer will break strict-aliasing rules"
* FBXReader.cpp - ‘boneLength’ may be used uninitialized in this function