treewide: be explicit about dependence on advice.h

Dozens of files made use of advice functions, without explicitly
including advice.h.  This made it more difficult to find which files
could remove a dependence on cache.h.  Make C files explicitly include
advice.h if they are using it.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/merge-recursive.c

@@ -1,5 +1,6 @@
 #include "cache.h"
 #include "builtin.h"
+#include "advice.h"
 #include "commit.h"
 #include "gettext.h"
 #include "tag.h"