RUBY-530 sasl gssapi support for MRI

We currently support kerberos authentication for JRuby.
This pull request adds a c extension that allows you to use Kerberos when on MRI.
yes, good eye = )
The java extension allows you to pass in canonicalize_host_name, so I set it here although it is not used so that the API is consistent between the two extensions. I figured it would be better to make it available to the c ext and perhaps make use of it later on, if I need to.