#18 No support to cancel SA queries

[Fabian Tillier]

While there cancelling SA queries is supported internally
to AL, there is no API that exposes this functionality to
clients. This can cause clients to time out on
destruction if an SA query is outstanding and they have
a limited time to clean up.

Supporting query cancellation requires adding a query
handle as an output parameter to ib_query, and adding
a new API that given an al_handle_t and a
query_handle_t cancels said query.