Update krb5 code to use glue routine lucid context functions

	The gssd code should not know about the glue layer's context structure.
	A previous patch added gss_export_lucid_sec_context() and
	gss_free_lucid_sec_context() functions to the gssapi glue layer.
	Use these functions rather than calling directly to the Kerberos
	gssapi code (which requires the Kerberos context handle rather
	than the glue's context handle).