Allow for creating raw diffs with cgit_print_diff()

This adds a parameter to cgit_print_diff() to create raw diffs, using
the same format as `git diff <commit>`.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>

ui-diff.c

@@ -358,7 +358,7 @@ void cgit_print_diff_ctrls()
 }
 
 void cgit_print_diff(const char *new_rev, const char *old_rev,
-		     const char *prefix, int show_ctrls)
+		     const char *prefix, int show_ctrls, int raw)
 {
 	enum object_type type;
 	unsigned long size;
@@ -398,6 +398,14 @@ void cgit_print_diff(const char *new_rev, const char *old_rev,
 		}
 	}
 
+	if (raw) {
+		ctx.page.mimetype = "text/plain";
+		cgit_print_http_headers(&ctx);
+		cgit_diff_tree(old_rev_sha1, new_rev_sha1, filepair_cb_raw,
+			       prefix, 0);
+		return;
+	}
+
 	use_ssdiff = ctx.qry.has_ssdiff ? ctx.qry.ssdiff : ctx.cfg.ssdiff;
 
 	if (show_ctrls)