- Increase the object lock's scope in vm_contig_launder() so that access

 - Increase the object lock's scope in vm_contig_launder() so that access
   to the object's type field and the call to vm_pageout_flush() are
   synchronized.
 - The above change allows for the eliminaton of the last parameter
   to vm_pageout_flush().
 - Synchronize access to the page's valid field in vm_pageout_flush()
   using the containing object's lock.