Simplify by reducing the "Node-action: replace" case to "Node-action:
add". This way, the main part of handle_node() only has to deal with
"add" and "change" nodes.
Functional change: replacing a symlink or executable without setting
properties will reset the mode.
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>