Bug report: sender needs to have backup-dir

[kenneth topp]

With this patch (see URL), backup-dir is passed to the server.  It's not 
currently ignored on the other end if irrelevant (which it is for 
senders).  Either we should not pass it, or let the sender ignore it 
later on.

http://cvs.samba.org/cgi-bin/cvsweb/rsync/options.c.diff?r1=1.109&r2=1.110&f=h

Either we should not pass it, or tell a sender to ignore it later on.  
Happy to whip up a patch either way...

Kenneth