Fix clang -Wextra except -Wunused-parameter.

Cleared all warnings that occur when passing
CFLAGS="-Wall -Wextra -Wno-unused-parameter" to make using clang 3.3 on
Linux x86-64.

i3bar/src/child.c

@@ -28,7 +28,7 @@
 #include "common.h"
 
 /* Global variables for child_*() */
-i3bar_child child = { 0 };
+i3bar_child child = {};
 
 /* stdin- and sigchild-watchers */
 ev_io    *stdin_io;