Allow gss_inquire_context on partial krb5 contexts

Allow gss_inquire_context on partial krb5 contexts

RFC 2743 states that gss_inquire_context() must always return flags,
locally_initiated, and open even if a context is not yet fully
established.  Additionally, a partially established context may also
return mech_type.

Previously, the krb5 mech raised an error for inquire_context on
partially completed contexts.  It now follows the rules layed out in
RFC 2743.

Add a new test program to verify that gss_inquire_context() works
correctly on both in-progress and established contexts.

[ghudson@mit.edu: minor style changes and commit message edits]

ticket: 8025