Fix build for FreeBSD 10.0

Move a rmlock.h inclusion up a bit so that the vm headers can get the
rmlock assertion (and other) macros they need.

The filedesc structure has been expanded on FreeBSD to support a
stronger capabilities system; getting to the actual file descriptor
requires another structure access.

limits.h and stdarg.h need sys/ and machine/ prefixes for inclusion in the
kernel on FreeBSD.  Unlike on master, there are not spurious include search
path directives to remove.

Catch up to VM layer changes.

This builds, but crashes at runtime due to some ABI incompatibilities
that appear in the rx event layer; those will be fixed in a separate patch.

Reviewed-on: http://gerrit.openafs.org/10339
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
(cherry picked from commit e222b08c4049dae95475eda2d5c54bd43dd45e2e)

Change-Id: Ia8f0f31b000292fd160b8752ad5839852e11f0e0
Reviewed-on: http://gerrit.openafs.org/10379
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>