Default option for :address should be :nil

This is very important, because we later assignment
  address = OPTIONS[:address] || generated_address
By using "" instead of :nil, we simply assign :address = empty
in any case
Close :fd immediately before running :exec
Fix some :if checks. Do not close :socket

Some :if checks are completely wrong because we change the value
to check without checking the boolean operator.

We close the :socket of some unknown reason. Do not know why that
really happens in the code. FIXME: This may cause another bug
New version 1.1.3