p9: add Twstat support to client

[DeedleFake]

Remote should have a WriteStat() method that performs wstat requests.

[DeedleFake]

Waiting on #19.

[DeedleFake]

#19 is done, but I think it makes more sense to add individual methods to Remote that handle different types of wstat requests, such as a Rename() method and a Chtimes() method.