Add a mechanism for the VFS layer to retry pathname resolution if a file
 system returns ESTALE at any point during the resolution process.  Pathname
 resolution is retried once from the first component, using all real lookup
 requests.

 This provides effective recovery for most cases where files or directories
 have been replaced by other remote file system clients.  It also provides
 a foundation to build a mechanism by which file system clients can fail
 over transparently to a replicated server.

 Test-plan:
 Combinations of rsync and "ls -l" on multiple clients.  No stale file handles
 should be after directory trees are replaced.  Standard performance tests;
 little or no loss of performance is expected.

 Created: Fri, 11 Feb 2005 16:46:19 -0500
Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>