To speed up Allegro (and other Lisp's that don't support inline

functions), change QUICK-TWO-SUM from a function to a macro.  Note
that macro has different calling convention than the function.  This
is needed because Allegro apparently doesn't handle VALUES without
boxing.

All rt tests pass.

qd-package.lisp:
o For CMUCL, don't import C::QUICK-TWO-SUM into the QDI package
  anymore.

qd-dd.lisp:
o New QUICK-TWO-SUM macro.

qd.lisp:
o Add CMUCL version of QUICK-TWO-SUM macro, which just calls
  C::QUICK-TWO-SUM.
o Update all users of QUICK-TWO-SUM appropriately.