1.0.7.3: non-consing GETHASH and (SETF GETHASH)

1.0.7.3: non-consing GETHASH and (SETF GETHASH)

 * Add a BLOCK for RETURN-FROM inside WITH-SPINLOCK-AND-WITHOUT-GCING,
   so that the compiler will not need to generate code to verify the
   tag existence at runtime -- which causes value-cell allocation.

   (Performance regression since new WITHOUT-INTERRUPTS implementation.)

 * Add a test-case to make sure basic hash-table functionality is non-consing.