Fix fd leak in DIR ccache cursor function

If dcc_ptcursor_next reached the end of a directory, it called free()
on the directory handle instead of closedir(), causing the directory
fd to be leaked.  Call closedir() instead.

ticket: 7573
target_version: 1.11.1
tags: pullup
Update acknowledgments in README

Also update copyright years.
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