Implement KERB_AP_OPTIONS_CBT (server side)

Add server support for Microsoft's KERB_AP_OPTIONS_CBT as described in
MS-KILE.  If the client includes the AP option in the authenticator
authdata and the server passed channel bindings, require the bindings
to match.

[ghudson@mit.edu: refactored to put more logic in the helper function;
added a comment; clarified commit message]

https://github.com/krb5/krb5/commit/4f7c77b64a048ca5e3199b26b31493698c777a9c
Author: Isaac Boukris <iboukris@gmail.com>
Committer: Greg Hudson <ghudson@mit.edu>
Commit: 4f7c77b64a048ca5e3199b26b31493698c777a9c
Branch: master
 src/include/krb5/krb5.hin                |    1 +
 src/lib/gssapi/krb5/accept_sec_context.c |   45 +++++++++++++++++++++++++++++-
 2 files changed, 45 insertions(+), 1 deletions(-)