NFS client bugfixes for Linux 3.5

Highlights include:

 - Fix a couple of mount regressions due to the recent cleanups.
 - Fix an Oops in the open recovery code
 - Fix an rpc_pipefs upcall hang that results from some of the
   net namespace work from 3.4.x (stable kernel candidate).
 - Fix a couple of write and o_direct regressions that were found
   at last weeks Bakeathon testing event in Ann Arbor.