patch applied (ghc): don't closeMutex() the Capability lock

[Simon Marlow]

Thu Aug 31 01:57:28 PDT 2006  Simon Marlow <simonmar at microsoft.com>
  * don't closeMutex() the Capability lock
  There might be threads in foreign calls that will attempt to return
  via resumeThread() and grab this lock, so we can't safely destroy it.
  
  Fixes one cause of
  
     internal error: ASSERTION FAILED: file Capability.c, line 90
  
  although I haven't repeated that assertion failure in the wild, only
  with a specially crafted test case, so I can't be sure I really got
  it.

    M ./rts/Capability.c -2 +4