merge.h: move declarations for merge.c from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/merge.c b/builtin/merge.c
index 8da3e46..6e8f7b9 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -37,6 +37,7 @@
 #include "color.h"
 #include "rerere.h"
 #include "help.h"
+#include "merge.h"
 #include "merge-recursive.h"
 #include "merge-ort-wrappers.h"
 #include "resolve-undo.h"