Fixes:

Async notifies received while a backend is in the middle of a begin/end
transaction block are lost by libpq when the final end command is issued.

The bug is in the routine PQexec of libpq. The routine throws away any
message from the backend when a message of type 'C' is received. This
type of message is sent when the result of a portal query command with
no tuples is returned. Unfortunately this is the case of the end command.
As all async notification are sent only when the transaction is finished,
if they are received in the middle of a transaction they are lost in the
libpq library. I added some tracing code to PQexec and this is the output:

Submitted by: Massimo Dal Zotto <dz@cs.unitn.it>