DERBY-6125 Code clean up in client driver.

Patch derby-6125-03-04-followup. Incorporates Knut's further
simplification suggestions for patches 03 and 04:

After the 04-a patch, these three methods in NetConnection do nothing except calling the method with the same name in the super class:

  - close()
  - closeX()
  - closeResources()

Removed, let NetConnection inherit them from its super class.

Make Connection.closeX() private and unsynchronized, as it will only
be called from Connection.close().

The patch also touches NetConnection's closeForReuse() method, which
doesn't have any callers. Removed.

Replaces System.arraycopy with Object.clone for byte array copies as
suggested.

NetConnection.completeConnect(): remove the override and make the
super method final instead.



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1464835 13f79535-47bb-0310-9956-ffa450edef68