* src/v5.c,src/v5.h(v5_creds_get_etype): remove the need for the
    	context pointer.
    * src/v5.c,src/v5.h(v5_creds_key_contents): return const data.
    * src/v5.c,src/v5.h(v5_creds_get_etype): add functions for picking
    	out principal name components and addresses and authdata from creds
    	structures.