Ensure that both Connection and XAConnection objects are closed. With Oracle, the XAConnection holds the physical database connection and a number of other caches which we need to release.
Merge pull request #25 from rankinc/close-connections

Ensure that both Connection and XAConnection objects are closed.  Clean fix.  Thanks.
Merge branch 'master' into fix-usage-count

Conflicts:
	btm/src/main/java/bitronix/tm/resource/jdbc/JdbcPooledConnection.java