Test the lock shape before falling into the thin lock code. The

Test the lock shape before falling into the thin lock code.  The
original formulation of this code relied on the subtly that the low
bit of a thread id is always 1 and so the shape bit was punned with
LSB of the thread id.  This got us two tests for the price of one.
When this code was moved forward to the new lock encoding scheme, we
did not crack the test in two.  This should correct the oversight.