saved_fmt = revs->diffopt.output_format;
revs->diffopt.output_format = DIFF_FORMAT_CALLBACK;
revs->diffopt.format_callback = cgit_diff_tree_cb;
saved_fmt = revs->diffopt.output_format;
revs->diffopt.output_format = DIFF_FORMAT_CALLBACK;
revs->diffopt.format_callback = cgit_diff_tree_cb;