btl/vader: bring up to date with fixes/updates from trunk

This commit brings the following commits from master:

open-mpi/ompi@12bfd13
open-mpi/ompi@79881ca
open-mpi/ompi@a31cf3b
open-mpi/ompi@13642f5
open-mpi/ompi@f56169c
open-mpi/ompi@1a3734a
open-mpi/ompi@13643f5
open-mpi/ompi@d60f0cb
open-mpi/ompi@75e8387

The most relevant changes:

 - Add support for KNEM. Allow selection of the single-copy mechanism
   at runtime. The default behavior has not changed. Vader will continue
   to use the best available mechanism. If the default mechanism is
   not available vader will fall back on another mechanism.

 - Improved CMA support. Code now determines if CMA can be used and
   (if possible) sets the appropriate ptrace permissions so it can
   be used.

 - Improved memory scaling by allocating fast box memory only once a
   send threshold has been met. This addresses an issue discovered by
   Riken.

 - Better fast-box design that further improves the small message
   performance.

Pieces of other relevant commits are also included in this commit.

Tested with XPMEM, CMA, and KNEM with Linux kernel 3.13.