KIdleTime is a global static, it's destructor it deletes the backend in
a deleteLater; This is *after* the app has been deleted.
This means we end up deleting Poller's ConnectionThread after the static
QVector managing the ConnectionThreads in the main app has been deleted,
leading to a confusing crash.
We can fix this by deleting the connection thread in unload rather than
the actual object destruction.
This fixes a crash on app close, most notably the recursive drkonqi
crash.