Update the Validator class so that the ensureNotNull method always throws
AssertionError if any of the arguments is null, rather than throwing a
NullPointerException if assertions were disabled and an AssertionError if
assertions were enabled.  Also, make the ensureTrue method always throw
AssertionError if the provided condition is not true rather than throwing an
IllegalArgumentException if assertions are disabled and AssertionError if
assertions are enabled.

Reviewed By:  David Ely
OpenDS Issue Number:  975