Regression in euca_conf --deregister-nodes

euca_conf --[de]register-nodes was changed in rev999 to be less brittle, by using a xsearch function rather than a grep to match IP to a list of IPs.

However it doesn't seem to work properly:
sudo euca_conf --deregister-node <IP> always returns: <IP> is not known (even when present).
The xsearch function apparently always returns false.

Note that sudo euca_conf --register-node <IP> also fails: it always adds the IP (even if it's already present), however the "uniq" call is preventing the same IP from appearing twice in the file, so the problem doesn't show.