Moved mouse capture handling into the server.

diff --git a/server/request.h b/server/request.h
index a6076d7..63aea54 100644
--- a/server/request.h
+++ b/server/request.h
@@ -264,6 +264,7 @@
 DECL_HANDLER(set_foreground_window);
 DECL_HANDLER(set_focus_window);
 DECL_HANDLER(set_active_window);
+DECL_HANDLER(set_capture_window);
 
 #ifdef WANT_REQUEST_HANDLERS
 
@@ -431,6 +432,7 @@
     (req_handler)req_set_foreground_window,
     (req_handler)req_set_focus_window,
     (req_handler)req_set_active_window,
+    (req_handler)req_set_capture_window,
 };
 #endif  /* WANT_REQUEST_HANDLERS */