Fixed the MLRISC bug sent by Markus Wenzel regarding the compilation
of Isabelle on the x86.

From Allen:
-----------
 I've found the problem:

     in ra-core.sml, I use the counter "blocked" to keep track of the
     true number of elements in the freeze queue.  When the counter goes
     to zero, I skip examining the queue.  But I've messed up the
     bookkeeping in combine():

         else ();
         case !ucol of
           PSEUDO => (if !cntv > 0 then
                 (if !cntu > 0 then blocked := !blocked - 1 else ();
                                    ^^^^^^^^^^^^^^^^^^^^^^^
                  moveu := mergeMoveList(!movev, !moveu)
                 )
              else ();

     combine() is called to coalesce two nodes u and v.
     I think I was thinking that if the move counts of u and v are both
     greater than zero then after they are coalesced then one node is
     removed from the freeze queue.  Apparently I was thinking that
     both u and v are of low degree, but that's clearly not necessarily true.


02/12/2002:
    Here's the patch.  HOL now compiles.

    I don't know how this impact on performance (compile
    time or runtime).  This bug caused the RA (especially on the x86)
    to go thru the potential spill phase when there are still nodes on the
    freeze queue.