1.0.43.47: Unfix ASH of constant shift on x86oids

1.0.43.47: Unfix ASH of constant shift on x86oids

 * The fixnum=>fixnum VOPs for ASH used to explicitly handle shifts greater
   than the word length by computing a zero instead.  These should be
   constant-folded away in IR1 now.

 * 1.0.43.45 incidentally fixed lp #309063 (which is what the fix above
   was used for). Add a test case, update NEWS, and note the optimizations
   committed in 1.0.43.{42,43,47}.