help PsychtoolboxKernelDriver - Mention new hacks needed for Yosemite

Need to disable global kext signature verification to make the driver
load.

Special thanks to the simple minded people at Cupertino for making life
even a bit more painful on your toy operating system.
help SyncTrouble - Mention how to disable compositor on KDE.

KDE/KWin may sometimes need to completely run without compositor on
some Intel gpu’s due to some problems with the latest ddx’es.

Note: KWin - at least in the version shipping in KUbuntu 14.10 - does
not auto-unredirect fullscreen windows if running on Intel gpu’s. This
according to Martin Graesslin to work around bugs in the Intel-ddx. Our
new-style-override redirect path, which is auto-selected on KDE +
Intel, can still force KWin to unredirect fullscreen windows / disable
composition, via proper XAtoms on our window. However, sometimes this
doesn’t seem to happen fast enough on some systems, so PTB throws some
timing warnings, which are spurious but still confusing to users.
Therefore a manual disable as described in “help SyncTrouble” might be
a better solution for users of Intel GPU’s on KDE/KWin.