builtin.h: Move two functions definitions to help.h.

The two functions defined here are implemented in help.c, so makes more sense
to put the definition of those in help.h instead of in builtin.h.

Signed-off-by: Thiago Farina <tfransosi@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git.c

@@ -1,6 +1,7 @@
 #include "builtin.h"
-#include "exec_cmd.h"
 #include "cache.h"
+#include "exec_cmd.h"
+#include "help.h"
 #include "quote.h"
 #include "run-command.h"