On a shutdown, deallocate the proper keep-alive connection ID.

It was deallocating the PoCo::Client::HTTP request ID, which isn't
coupled to the PoCo::Client::Keepalive ID at all.

The problem wasn't apparent before because IDs were coincidentally in
synch.  Recent changes finally desynchronized them.
Provide a dummy version number for development testing.

The default connection string is based on the component version, which
stopped being defined in-house since the move to Dist::Zilla.  Tests
were noisy and ugly with moot "uninitialized value" warnings.