SASL support for LDAP back end

Here are Zoran's patches for LDAP SASL support, as submitted to krbdev@mit.edu in October 2013.

Per our new workflow, I am converting the submission to a pull request.  This will need a lot of work before it will be ready for final review, including but not limited to:

* The patches are against 1.11, not master.  I did a lot of work on the LDAP KDB module in early 2013 after 1.11 was released, so it won't be a trivial merge.

* There are numerous style issues, and the commit messages are much too verbose.

* The profile changes need careful attention to ensure that they are backward-compatible and use appropriate naming.

* We will need a project page.  I started one at http://k5wiki.kerberos.org/wiki/Projects/LDAP_SASL_TLS_support back in January 2013 but it's just a stub.