Parallel I/O extensions to namei backend

Parallel I/O extensions to namei backend

This adds the ability for certain namei operations (currently only
ListViceInodes) to occur across multiple different threads in
parallel. Currently this is only enabled when built with the
not-yet-existant AFS_SALSRV_ENV.

Originally written by Tom Keiser.

(cherry picked from commit 0a4a03ae68bea51a74a4ef496d50a800bd3e0cbd)
Reviewed-on: http://gerrit.openafs.org/1864
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
Change-Id: I2fa3aa60a13c81e0a0bc7ffb5b323ec7580f560f
Reviewed-on: http://gerrit.openafs.org/3826
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>