Port Linux events to SDL

New CVar "in_kbd" to set the layout for the keyboard. SDL 1.2
doesn't offer any way to determine it, and we need this feature
to use the same key for toggling the console independent of the
keyboard layout.
The old "in_nograb" from the Linux backend is still supported.

CMakeLists.txt

@@ -675,6 +675,7 @@ else()
 	set(src_sys_base
 		sys/cpu.cpp
 		sys/threads.cpp
+		sys/events.cpp
 		sys/sys_local.cpp
 		sys/posix/posix_net.cpp
 		sys/posix/posix_signal.cpp
@@ -685,8 +686,6 @@ else()
 	set(src_sys_core
 		${src_stub_util}
 		sys/glimp.cpp
-		sys/posix/posix_input.cpp
-		sys/linux/input.cpp
 	)
 endif()