Fix typo in JCite spec

git-svn-id: https://svn.forgerock.org/opendj/trunk/opendj@11198 41b1ffd8-f28e-4786-ab96-9950f0a78031
ByteString.java:
In several methods added short circuit checks to return the EMPTY ByteString instance.
In valueOfHex(), simplified the code by directly returning the EMPTY ByteString instance.
Removed local variables.
Removed uneeded parentheses.

ByteStringTestCase.java:
Added two test cases.

git-svn-id: https://svn.forgerock.org/opendj/trunk/opendj@11205 41b1ffd8-f28e-4786-ab96-9950f0a78031