Kerberos, GSSAPI and KADM5 bindings

Features:
+ An interface for maintaining credential caches (KRB5CCache),
   that can be used for authenticating against a kerberos5 realm
+ Bindings for nearly the complete GSSAPI (RFC2744)
+ The administrative interface (KADM5)
+ Support for HTTP Negotiate authentication via GSSAPI

Documentation:
+ see docs/ for the API documentation
+ there are several pieces of example code in the examples/ directory
+ see below for install instructions
