Incorporate review feedback into security pieces of JKernel:

   1) Avoid unnecessary code:
       a) Optimization in StandaloneByteArrayAccess (stripped out)
       b) Usage of custom digest stream classes (omitted)
   2) sun.jkernel.StandaloneSHA class should be package private
   3) StandaloneMessageDigest should guard itself against bypassing its factory method.
   4) DownloadManager and SplitJRE should use StandaloneMessageDigest directly.
   5) Unit tests accidently left out of the external code review and integration
      putback are included, with a few small improvements. (See the CR 6572493 j2se
      webrev URL for the originals)
        test/sun/jkernel/DownloadManager/ParallelClassloading.java
        test/sun/jkernel/StandaloneMessageDigest/ByteArrayToFromHexDigits.java
        test/sun/jkernel/StandaloneMessageDigest/MeasureStandaloneMessageDigest.java
        test/sun/jkernel/StandaloneMessageDigest/StandaloneMessageDigest.java