Fix modifier keys.

The wrong mask was used making all modifier keys not be recognized.
Fallback for sendEvent command key fix.

If an NSApplication is created before GLFW is initialized, [GLFWApplication sharedApplication] does nothing and the sendEvent command key fix is not used. This commit works around the issue by sending a key up event immediately. Without this, no key up event is ever sent (which is very bad!).
Undecorated window support on win/mac/linux.