[project @ 2006-01-03 12:56:10 by simonmar]

two fixes for the case when a (synchronous) exception is propagated to
the top of a thread's stack, i.e. it is unhandled.

  1. store the exception in the right place (we were using the
     OFFSET_StgTSO_stack macro and not accounting for the TSO's
     header size)

  2. put an stg_enter_info on the stack so that the GC can understand
     this thread's stack.