1.0.7.19: SB-EXT:COMPARE-AND-SWAP

1.0.7.19: SB-EXT:COMPARE-AND-SWAP

 * New macro SB-EXT:COMPARE-AND-SWAP provides a supported interface to
   compare-and-swap functionality.

 * New info-type :FUNCTION :STRUCTURE-ACCESSOR allows us to map from
   defstruct slot-accessor names to defstruct descriptions.

 * Add :CAS-TRANS slot keyword to DEFINE-PRIMITIVE object, and the
   compiler machinery needed to support compare and swap on primitive
   object slots.

 * New VOPs COMPARE-AND-SWAP-SLOT and %COMPARE-AND-SWAP-SYMBOL-VALUE.

 * Delete now unnecessary DEFINE-STRUCTURE-SLOT-COMPARE-AND-SWAP.

 * Use a consistent %COMPARE-AND-SWAP-FOO naming scheme for CAS
   functions.

 * Tests.

 Tested on x86/Linux & x86/Darwin, x86-64/Darwi, and PPC/Darwin.