Add knc_get_service()

And make knc_get_{client, service}() work symmetrically, calling
gss_inquire_context() as needed (and always on the service side), but
only once per-context.
Minor update to liknc.3 regarding naming
Add knc_free_deleg_cred()

And note that knc_set_cred() can be used to release credentials set
earlier.  This is useful when one wants to keep a security context but
drop privs and access to privileged credentials.
Unexpand tabs
knc(1) should export name and mechanism OID