0.9.16.28:

0.9.16.28:
	Shorten pseudo-atomic sequence on x86 and x86-64.

	Do this by combining *pseudo-atomic-{atomic,interrupted}* into
	  a single variable, *pseudo-atomic-bits*, which is a fixnum
	  bitmask where bit 0 denotes atomic-ness and bit 1 denotes
	  interruptedness.
	* Change genesis to initialize this variable properly (this
	  didn't need to be done for the old variables because the
	  allocation sequences would set them upon entrance);
	* Modify functions and macros accessing pseudo-atomic variables
	  to reflect the new state of the world;