fix zlib include path in zip.h
Support resizing windows + improve fullscreen for SDL2

By implementing GLimp_SetScreenParms() and enhancing the
event handling
Support resizing windows for SDL1.2

By implementing GLimp_SetScreenParms() for SDL1.2
and enhancing the event handling
support ctrl-g for (un)grabbing mouse

Many Linux Games support that
Pause when window loses focus, introduce com_pause

If the window loses focus com_pause is set to 1, when it regains focus
it's set to 0.
The behaviour on Win32 stayed the same (the implementation is less
hacky though) and Linux now matchces that.
Fix Sys_ListFiles() on POSIX once again

Turned out that as "extension" (which is really more like a pattern
that matches the whole file) was even used with patterns like "*.*"
so we do proper matching using fnmatch() now - which is even easier
than the old way.
Now deleting savegames on POSIX works.
Precompiled Headers for GCC+Clang
Merge remote-tracking branch 'DanielGibson/improve-window-handling'
Merge remote-tracking branch 'DanielGibson/gcc-pch'
Merge branch 'master' into openal