Change app finalizer to callback to match celluloid 0.13.0
Add more socket error rescue clauses

A few more things could go wrong than I had previously accounted for. Rescue
those errors as well and log where appropriate.
Bump celluloid-io dependency to 0.13.1

This should fix a problem with improper handling of prematurely closed
connections. There was a bug where, if ringleader hadn't yet gotten around to
proxying a socket before it was closed, an IOError would be raised from within
celluloid itself, and it was impossible to rescue from this situation.
Bump version to 1.1.5.pre1