Fix reported in
bug #327, comment #3 - untested but seems reasonable/safe.
Mark team for deletion when letting others know it has left during game. Should help with quitters problem.
reimplemented ResetKbd and calling it when exiting gsChat status, this restores behavior from.17: You can now walk -> press t/chat -> type some stuff while still walking -> exit gsChat and stop walking at that moment
add NOPNG to cmake to explicitly disable PNG dependency
reorganise osx detection and variable initalization (simpler crosscompiling) in cmake