Resync Autoconf macros from rra-c-util 3.3
This includes the following fixes:
* Include krb5.h before probing for the IBM-specific header file for
obtaining error strings to avoid Autoconf warnings on AIX.
* Use [] to mark empty arguments to Autoconf macros.
* Add an explicit license statement to these Autoconf macros, matching
the normal Autoconf macro license.
* Ensure rra_use_kerberos is always set so that other parts of configure
can rely on it.
Change-Id: I521d38ad6834808cf09c798aeba0efc0dd741fd6
Reviewed-on: http://gerrit.openafs.org/4588
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>