a few more minor stuff from uhexen2 svn

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1133 af15c1b1-3010-417e-b628-4374ebc0bcbd
quakespasm.pak: More z-fighting workarounds.

This fixes:

e1m4:
- The secret doors in the room with the five quake-logo buttons on the floor (when open).

e2m2:
- The platform in the water behind the gold key door (when down).
- The wallpiece that pushes the player into the gold key room (when "closed").


git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1134 af15c1b1-3010-417e-b628-4374ebc0bcbd
quakespasm.pak: More z-fighting workarounds.

This fixes:

e2m3:
- The floorpiece (when down) and wallpiece (when open) by the crates opposite the normal exit.


git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1135 af15c1b1-3010-417e-b628-4374ebc0bcbd
quakespasm.pak: Another z-fighting workaround.

This fixes:

e2m3:
- The wallpiece that blocks the way out of the Well of Wishes (when open).


git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1136 af15c1b1-3010-417e-b628-4374ebc0bcbd
GL_Init: on OS X, enable multi-threaded OpenGL mode.

This moves some of the OpenGL implementation to a background thread, and makes draw calls block for a shorter amount of time. AFAIK, this is the default mode on most other OS'es, not sure why you have to explicitly ask for it on OS X.

N.B. the kCGLCEMPEngine constant is available on 10.4+ so I don't bother checking the OS X version.
More info: https://developer.apple.com/library/mac/technotes/tn2085/_index.html

git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk@1137 af15c1b1-3010-417e-b628-4374ebc0bcbd