Sentinel

S (Sentinel) is tested and set with the kill and isSentinel methods.
kill is never called therfore S is never in the table but isSentinel is called by
get_impl,casValueSlot,opSizeCntr
Thus this functions are not functional.
Reason is that I wrote some of the code according to the slides witch include sentinel.
And the resize code according to the java implmentation with only uses tombstone.
