Return an error for invalid savedata sizes.

May fix WALL-E according to:
http://forums.ppsspp.org/showthread.php?tid=434
Fix Qt build on x86 and probably NEON.
Poll controllers on a separate thread on Windows.

This means controllers will sample more than the game fps, and will work
whenever keyboards do.
Merge pull request #5707 from unknownbrackets/savedata

Return an error for invalid savedata sizes
Merge pull request #5706 from unknownbrackets/win-input

Poll controllers on a separate thread on Windows
Apply the volatile mem thread on the right thread.

Inside __KernelVolatileMemLock(), it applies also when unlocking when
waking another thread.  This was causing the tests to hang and die.
Fix a typo.

Not sure how this one happened...
Initial stab at tracking vertex alpha.

Not sure what efficient method to use on x86...
Switch to fullAlphaReg not hasAlphaReg.