PTB BETA RELEASE "Hammertime!" SP3 - "Flowerpower"

* Fix Linux X11 display locking bugs which could cause deadlock in Screen('Resolutions'), and crashes for Screen('AsyncFlipBegin') async flips and framesequential stereo mode 11. These bugs could only affect the Mesa/Gallium FOSS graphics drivers, therefore slipped through the testing which was performed with the NVidia binary blob. Retesting on nouveau exposed the bugs.

-> Our locking bugs should be fixed without degradation in performance.
-> There are other bugs which can cause crashes at least with MultiWindowLockStepTest(n) for n > 1. These look like bugs in nouveau,
-> This release was validated on the upcoming Ubuntu 13.10 "Saucy Salamander" 64-Bit Beta with nouveau.