DERBY-6125 Code clean up in client driver.

    Patch derby-6125-03-a. This patch

    - makes a mutable public array (dncPackageConsistencyToken) private.
    - removes a couple of assignment with values that are never used (e.g. myPVH)
    - makes some members final and public
    - reworks an invariant to use SanityManager assert
    - replaces a StringBuffer with StringBuilder
    - makes a lazy initialization thread safe (codePointNameTable__)
    - removes a couple of noop bit operations
    - removes an unused method (computeDncLogWriter with existing connection overload)

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1463079 13f79535-47bb-0310-9956-ffa450edef68