Add awesome.sync()

This function should only be necessary for the test suite. It makes sure
that the X11 server received and handled all previous requests that
awesome sent. This will be needed, for example, in tests that use
root.fake_input().

After a call to awesome.sync(), we are sure that "faking input" has been
done and the next main loop iteration will handle the input event.
Without the sync, it could happen that the X11 server did not yet fake
the input in the next iteration.

Signed-off-by: Uli Schlachter <psychon@znc.in>

luaa.c

@@ -54,6 +54,7 @@
 #include <basedir_fs.h>
 
 #include <xcb/xcb_atom.h>
+#include <xcb/xcb_aux.h>
 
 #include <unistd.h> /* for gethostname() */
 
@@ -214,6 +215,17 @@ luaA_kill(lua_State *L)
     return 1;
 }
 
+/** Synchronize with the X11 server. This is needed in the test suite to avoid
+ * some race conditions. You should never need to use this function.
+ * @function sync
+ */
+static int
+luaA_sync(lua_State *L)
+{
+    xcb_aux_sync(globalconf.connection);
+    return 0;
+}
+
 /** Load an image from a given path.
  *
  * @param name The file name.
@@ -647,6 +659,7 @@ luaA_init(xdgHandle* xdg, string_array_t *searchpath)
         { "xkb_get_group_names", luaA_xkb_get_group_names},
         { "xrdb_get_value", luaA_xrdb_get_value},
         { "kill", luaA_kill},
+        { "sync", luaA_sync},
         { NULL, NULL }
     };