Set debug level to line numbers only.
Remove redundant (duplicate) __init() call injected into constructors.
Switch _isClosed volatile boolean to a ThreadLocal instead.  This allows us to handle the
case where a consumer tries to continue to use a connection after it has been returned
to the pool and dispatched to another consumer.  Previously, when the new consumer
received the connection, the _isClosed boolean would be reset, allowing an old consumer
to invoke against it without error.  Now due to the ThreadLocal, and old consumer will
still continue to see the connection as being in the closed state, even when it has become
“unclosed” for another consumer.