Make rev-list flush the stdio buffers after each rev.

We'd rather get the revisions in a slow but timely manner than
have to wait for them.

rev-list.c

@@ -64,6 +64,7 @@ static void show_commit(struct commit *commit)
 		pretty_print_commit(commit_format, commit->buffer, ~0, pretty_header, sizeof(pretty_header));
 		printf("%s%c", pretty_header, hdr_termination);
 	}
+	fflush(stdout);
 }
 
 static int filter_commit(struct commit * commit)