Fix T62114: Wireframe mode selection: selects backside objects when clicking frontside object in 3d-window

Now the depth order of objects when trying to select them is only used when not in X-ray mode.
Before, this was only the case in wireframe mode regardless of X-ray settings.

I've also unified the usage of V3D_XRAY and XRAY_FLAG as they were basically copies of each other.

Reviewed By: Clément

Differential Revision: http://developer.blender.org/D4504

source/blender/draw/modes/pose_mode.c

@@ -27,6 +27,8 @@
 #include "DRW_engine.h"
 #include "DRW_render.h"
 
+#include "ED_view3d.h"
+
 /* If builtin shaders are needed */
 #include "GPU_shader.h"