QPID-5139: HA correct compile error on older C++ compilers.

- Added constructors for AsyncCompletion::Callback so subclasses can be copied.
- Get rid of intrusive_ptr::reset

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1537187 13f79535-47bb-0310-9956-ffa450edef68
NO-JIRA: Fix compile errors in legacystore on older compilers

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1537188 13f79535-47bb-0310-9956-ffa450edef68