Add localauth pluggable interface

Add a new pluggable interface for local authorization, and replace the
existing krb5_aname_to_localname and krb5_kuserok implementations with
implementations based on the pluggable interface.

ticket: 7583 (new)
Add tests for localauth interface

Create a test module, program, and script to exercise the
krb5_aname_to_localname and krb5_k5userok functions as well as the
localauth pluggable interface.

ticket: 7583
Document localauth interface

ticket: 7583
Remove stray include in localauth_plugin.h

This unnecessary include was causing build failures on some systems by
making libkrb5 sources depend on gssapi.h.
Add support for k5srvutil -e keysalts

k5srvutil is a little more convenient to use for rolling keys than
kadmin is.  When migrating off 1DES, though, it may be desirable to
explicitly specify the desired keysalts.  This adds an option, -e, to
k5srvutil to specify desired keysalts.

[ghudson@mit.edu: style fix; make whitespace in keysalt list work]

ticket: 7589 (new)
Initialize status in krb5_ldap_parse_db_params

If db_args is non-null but empty, status could be returned without
being initialized; gcc with optimization correctly warns about this,
causing a build failure.  (This bug was introduced by
0b1dc2f93da4c860dd27f1ac997617b712dff383 which was pushed after the
1.11 release branch, so it isn't in any release.)