diff.h: move declaration for global in diff.c from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -523,9 +523,6 @@ int add_files_to_cache(struct repository *repo, const char *prefix,
 		       const struct pathspec *pathspec, int include_sparse,
 		       int flags);
 
-/* diff.c */
-extern int diff_auto_refresh_index;
-
 /* ls-files */
 void overlay_tree_on_index(struct index_state *istate,
 			   const char *tree_name, const char *prefix);

diff.h

@@ -701,4 +701,6 @@ void print_stat_summary(FILE *fp, int files,
 			int insertions, int deletions);
 void setup_diff_pager(struct diff_options *);
 
+extern int diff_auto_refresh_index;
+
 #endif /* DIFF_H */