afsadminutil: translate krb5 error messages on Windows

afsadminutil: translate krb5 error messages on Windows

util_AdminErrorCodeTranslate() is used to translate error
code messages within the libadmin library set and is used
by translate_et.  This has in the past not translated
krb5 error codes.

This patchset conditionally adds support for using
krb5_get_error_message() or error_message() on the Windows
platform if KFW is installed.  This is accomplished by
adding new functions to afsutil.lib:

  initialize_krb5()
  fetch_krb5_error_message()

which are used within util_AdminErrorCodeTranslate()
only if AFS_KRB5_ERROR_ENV is defined.

Support for Unix is not provided at the present time
because doing this "right" will lead to a dependence on
kerberos libraries from this library, which we might want
to avoid.

Change-Id: I7caf7b8e41cfd806f4defc175aa45afb165ec244
Reviewed-on: http://gerrit.openafs.org/1531
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>