This patch equips the 'Block::Connection' with a framework API for the
implementation of robust block-session clients that perform block I/O in
an asynchronous fashion.
An application-defined 'JOB' type, inherited from 'Connection::Job',
encapsulates the application's context information associated with a
block operation.
The lifecycle of the jobs is implemented by the 'Connection' and driven
by the application's invokation of 'Connection::update_jobs'. The
'update_jobs' mechanism takes three hook functions as arguments, which
implement the applications-defined policy for producing and consuming
data, and for the completion of jobs.
Issue #3283
784206c85c