patch applied (ghc): MERGE: Fix bug exposed by conc052.

[Simon Marlow]

Wed Apr  4 03:30:27 PDT 2007  Simon Marlow <simonmar at microsoft.com>
  * MERGE: Fix bug exposed by conc052.
  A thread that was blocked on a blackhole but can now be woken up could
  possibly be treated as unreachable by the GC, and sent the
  NonTermination exception.
  
  This can give rise to spurious <<loop>>s in concurrent programs, so
  it's a good one to fix.

    M ./rts/sm/MarkWeak.c -5 +14