copy.h: move declarations for copy.c functions from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 0621f6f..0b411e9 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -2,6 +2,7 @@
 #include "abspath.h"
 #include "checkout.h"
 #include "config.h"
+#include "copy.h"
 #include "builtin.h"
 #include "dir.h"
 #include "environment.h"