start_command(), .in/.out/.err = -1: Callers must close the file descriptor

By setting .in, .out, or .err members of struct child_process to -1, the
callers of start_command() can request that a pipe is allocated that talks
to the child process and one end is returned by replacing -1 with the
file descriptor.

Previously, a flag was set (for .in and .out, but not .err) to signal
finish_command() to close the pipe end that start_command() had handed out,
so it was optional for callers to close the pipe, and many already do so.
Now we make it mandatory to close the pipe.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

bundle.c

@@ -333,6 +333,7 @@ int create_bundle(struct bundle_header *header, const char *path,
 		write_or_die(rls.in, sha1_to_hex(object->sha1), 40);
 		write_or_die(rls.in, "\n", 1);
 	}
+	close(rls.in);
 	if (finish_command(&rls))
 		return error ("pack-objects died");