Disable deprecated warnings for krb5 routines

In OS X 10.9 Mavericks, Apple has marked all of the krb5 routines
as deprecated (in favor of the GSS framework).  We must disable
these warnings in order to allow the buildslave to have a successful
build.

Luckily, Apple has left in rope for us to programmatically disable
the deprecated attribute with a preprocessor macro.  Defining this
macro should be safe everywhere, so do so unconditionally.

This commit touches a few more files than the version on master does,
since the 1.6 branch is using the krb5 library for its rxkad-k5
implementation; the files in auth/ and rxkad/ are specific to 1.6.

Reviewed-on: http://gerrit.openafs.org/10699
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
(cherry picked from commit 17c50911f79382e3ba8960e4b6c122b348e9baef)

Change-Id: Id0e806029e25583698574bf3df626ce12a72312a
Reviewed-on: http://gerrit.openafs.org/10735
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>