patch applied (ghc): Eagerly raise a blocked exception when entering ' unblock' or exiting ' block'

[Simon Marlow]

Fri Jan  5 05:57:15 PST 2007  Simon Marlow <simonmar at microsoft.com>
  * Eagerly raise a blocked exception when entering 'unblock' or exiting 'block'
  This fixes #1047

    M ./rts/Exception.cmm -5 +50
    M ./rts/RaiseAsync.c -2 +6
    M ./rts/RaiseAsync.h -1 +1