Merge pull request #37 from Psychtoolbox-3/master

Resync with current master of official Psychtoolbox-3 repo.
Screen/OSX: Down allow closing of kPsychGUIWindows by user.

Disable the window close button, as clicking it would crash the
scripting environment at next access after window close.
-> Screen for Octave and Matlab on OSX rebuilt and tested.
Screen/Windows: Allow activation of GUI windows via mouse click.

kPsychGUIWindow's return MA_ACTIVATEANDEAT in response to mouse
activation events, as opposed to MA_NOACTIVATEANDEAT for other windows.

-> Clicking an inactive GUI window will activate it.
-> Also apply minor fix to DWM timestamping in the rare cases where it can
   be used and doesn't work, e.g., compositor active on a single display,
   single onscreen window setup (where it can be used), but inside a Windows-7
   VM, where it fails with invalid values on VirtualBox. We double-check timestamp
   for validity and return a failure code on invalid timestamp, so fallback path
   can be used.
-> Various dead code removal.

-> Screen for 32/64-Bit Matlab on Windows rebuilt and tested.

Fixes #156
Merge pull request #160 from kleinerm/master

Pull from kleinerm for PTB BETA RELEASE "Blue skies and empty brains" - SP3
* GUI window mode fixes for OSX and MS-Windows.