PROTON-1588: c++ libuv proactor release_connection bug
PROTON-1588: c++ libuv proactor release_connection bug

Untangle lifecycles, get rid of proton refcounts for the pconnection_t.
The pconnection_t and pn_connection_t can now be completely separated,
the former always belongs to the proactor, the latter may be given back
to the user by pn_proactor_release_connection().

alanconway/qpid-proton,apache/qpid-proton,ssorj/qpid-proton,apache/qpid-proton,apache/qpid-proton,kgiusti/qpid-proton,ssorj/qpid-proton,alanconway/qpid-proton,astitcher/qpid-proton,alanconway/qpid-proton,kgiusti/qpid-proton,kgiusti/qpid-proton,gemmellr/qpid-proton,astitcher/qpid-proton,astitcher/qpid-proton,apache/qpid-proton,gemmellr/qpid-proton,apache/qpid-proton,ChugR/qpid-proton,ChugR/qpid-proton,alanconway/qpid-proton,gemmellr/qpid-proton,ssorj/qpid-proton,ssorj/qpid-proton,ChugR/qpid-proton,gemmellr/qpid-proton,alanconway/qpid-proton,apache/qpid-proton,ssorj/qpid-proton,astitcher/qpid-proton,alanconway/qpid-proton,ChugR/qpid-proton,astitcher/qpid-proton,astitcher/qpid-proton,ssorj/qpid-proton,kgiusti/qpid-proton,gemmellr/qpid-proton,gemmellr/qpid-proton,ChugR/qpid-proton,kgiusti/qpid-proton,ChugR/qpid-proton,kgiusti/qpid-proton