tombailo authored Jul 15, 2019 and Claudio Saavedra committed Aug 22, 2019

This commit changes the way the user-supplied GCancellable is handled in
the implementation of soup_session_send_async() and soup_session_send().
Previously the user-supplied GCancellable replaced the instance on the
SoupMessageQueueItem used to queue the request. In the event of a
request being internally re-queued, the GCancellable would be
reset, which was problematic if the GCancellable had been passed in by
client code which might be using the same instance to cancel soup
requests and to perform application-specific  cancellation.

This commit changes the implementation of the above two functions so
that the user-supplied instance is chained to the internal instance via
a callback so that cancelling it cancels the internal instance while the
two objects can maintain their own state.

A test to test the use of a cancellable with soup_session_send() is also
added to connection-test.c.