v4: Protect LDAP connections from being freed when there are outstanding queries...

v4: Protect LDAP connections from being freed when there are outstanding queries... (#4267)

* Use correct DN string in debug message

* Use query type to identify LDAP searches

* Protect fr_ldap_connection_t from being freed if there are pending queries

* Add watcher checking for outstanding queries when an LDAP connection closes

* Alter _ldap_query_free() to free the associated connection if it is closed ...

... and has no other queries associated with it

* Queries are removed from the pending tree by the query destructor

* Improve handling of un-expected results retrieved from libldap

* Don't free LDAP results just because an LDAP error was returned ...

... if the caller wants the results, it may want to query them
regardless of success or failure.

* Add debug message for auth bind reject

* Free the bind_auth_ctx when we've finished with it

* Improved version of _ldap_bind_auth_io_read()

- handle fr_ldap_result() returning no result
- handle LDAP_PROC_REJECT
- use a normal while loop