Update ap-auth-kerb to 5.4.

Changes:
* implemented KrbServiceName Any to deal with multiple keytab entries for
  various browsers
* implemented KrbLocalUserMapping i.e. to strip @REALM from username for
  further use
* implemented already_succeeded function to avoid hammering the KDC with
  same auth requests in single connection
* fixed threading issues
* improved configure and Makefile scripts (mainly for BSD users)
* fixed minor issues

(minskim)