Improving error chaining.

If the transport is lost to an error and that causes all the channels to close, we want the error at the transport to be chained when reporting a channel closed error.
Send logging to java.util.logging instead of inventing own logging scheme.

This allows the user to control logging level selectively for different subsystems. It requires no program change to activate logging.
Log level adjustment

In mapping log level to j.u.l, 20 is INFO which gets reported by default, so we want to keep them only for abnormal situations.

These messages get reported during normal operation, so downgrading the logging level here to avoid clutter
Pass exceptions to the logger
Revisiting the logging level.

I noticed that TransportManager.receiveLoop never returns normally and so as it stands now we end up always reporting a warning, even during the normal termination of a connection.

Since trilead is meant to be a general purpose library, it is not desirable for it to produce any logging in the default JVM setting,
which means >=INFO is not OK.

Toning down the whole level by a notch to satisfy this constraint. We can still selectively enable logging levels to get details captured.
If the connection is closed from this side, don't report that.

The close() call closes the socket, which results in the following exception:

java.net.SocketException: Socket closed
	at java.net.SocketInputStream.socketRead0(Native Method)
	at java.net.SocketInputStream.read(SocketInputStream.java:150)
	at java.net.SocketInputStream.read(SocketInputStream.java:121)
	at com.trilead.ssh2.crypto.cipher.CipherInputStream.fill_buffer(CipherInputStream.java:41)
	at com.trilead.ssh2.crypto.cipher.CipherInputStream.internal_read(CipherInputStream.java:52)
	at com.trilead.ssh2.crypto.cipher.CipherInputStream.getBlock(CipherInputStream.java:79)
	at com.trilead.ssh2.crypto.cipher.CipherInputStream.read(CipherInputStream.java:108)
	at com.trilead.ssh2.transport.TransportConnection.receiveMessage(TransportConnection.java:232)
	at com.trilead.ssh2.transport.TransportManager.receiveLoop(TransportManager.java:685)
	at com.trilead.ssh2.transport.TransportManager$1.run(TransportManager.java:481)
	at java.lang.Thread.run(Thread.java:722)