Add shared diff-handling functions

This adds a standard interface for tree diffing.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.h

@@ -19,6 +19,7 @@
 
 
 typedef void (*configfn)(const char *name, const char *value);
+typedef void (*filepair_fn)(struct diff_filepair *pair);
 
 struct cacheitem {
 	char *name;
@@ -116,6 +117,10 @@ extern int chk_positive(int result, char *msg);
 extern int hextoint(char c);
 
 extern void *cgit_free_commitinfo(struct commitinfo *info);
+extern void cgit_diff_tree(const unsigned char *old_sha1,
+			   const unsigned char *new_sha1,
+			   filepair_fn fn);
+extern void cgit_diff_commit(struct commit *commit, filepair_fn fn);
 
 extern char *fmt(const char *format,...);