This patch fixes a potential data inconsistency which may occur when
using AdvFS directIO.  The following scenario has been shown to
occassionally recreate this problem.

	- application (e.g. Oracle) is performing the following operation
		- issue a pwrite() to write a DB block 
		  (and save the buffer away)
		- issue a pread() for this very block
		- incorrect/different data is returned 
		  ie. not the one written by the pwrite()
    		- Now if the pwrite() using the "old" buffer
		  is repeated and another pread() is issued
		  the correct data is returned


