Query whether an Aio remains unresolved. This is an experimental technical
utility version of unresolved not intended for ordinary
use. Provides a method of querying the busy status of an Aio without
altering its state in any way i.e. not attempting to retrieve the result
or message.
.unresolved(aio)an Aio (object of class 'sendAio' or 'recvAio').
Logical TRUE if 'aio' is an unresolved Aio, or FALSE otherwise.
.unresolved() is not intended to be used for 'recvAio'
returned by a signalling function, in which case unresolved
must be used in all cases.