Initial set of changes for El Capitan OS X 10.11 .

Initial set of changes for El Capitan OS X 10.11 .

Mainly new El Capitan specific config files and defitions of
Darwin 15 variables and config tests/etc.

Reviewed-on: http://gerrit.openafs.org/12072
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
(cherry picked from commit bf3707ccbf98f44103171f4a5c6fb5bcd0744bfc)

Change-Id: I96c6c451841081d26a101507f35ff86fc8c54771
Reviewed-on: https://gerrit.openafs.org/12212
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Marcio Brito Barbosa <mbarbosa@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>