Add externs to interface and class headers.

Signed-off-by: aixxe <me@aixxe.net>

include/cstrike/Interfaces/IPanel.h

@@ -11,4 +11,6 @@ class IPanel {
 		void PaintTraverse(VPANEL vpanel, bool force_repaint, bool allow_force) {
 			GetVirtualFunction<void(*)(IPanel*, VPANEL, bool, bool)>(this, 42)(this, vpanel, force_repaint, allow_force);
 		}
-};
+};
+
+extern IPanel* panel;