Fix DBCP-355.
Ensure that the XAConnection is closed when the associated Connection is closed.
Based on a patch by Florent Guillaume.
        

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/dbcp/branches/DBCP_1_5_x_BRANCH@1563895 13f79535-47bb-0310-9956-ffa450edef68