* src/lib/gssapi/mechglue/mglueP.h: Add loopback field to opaque

	* src/lib/gssapi/mechglue/mglueP.h: Add loopback field to opaque
	structs of gss_ctx_id_t, gss_name_t, gss_cred_id_t to catch some
	application programming errors.  Add new macro GSSINT_CHK_LOOP()
	which returns non-zero if loopback field doesn't point to itself.

	* src/lib/gssapi/mechglue/g_accept_sec_context.c
	(gss_accept_sec_context):
	* src/lib/gssapi/mechglue/g_acquire_cred.c (gss_add_cred)
	(gss_acquire_cred):
	* src/lib/gssapi/mechglue/g_delete_sec_context.c
	(gss_delete_sec_context):
	* src/lib/gssapi/mechglue/g_glue.c
	(gssint_convert_name_to_union_name):
	* src/lib/gssapi/mechglue/g_imp_name.c (gss_import_name):
	* src/lib/gssapi/mechglue/g_imp_sec_context.c
	(gss_import_sec_context):
	* src/lib/gssapi/mechglue/g_init_sec_context.c
	(gss_init_sec_context): Set loopback pointers.

	* src/lib/gssapi/mechglue/g_delete_sec_context.c
	(gss_delete_sec_context):
	* src/lib/gssapi/mechglue/g_rel_cred.c (gss_release_cred):
	* src/lib/gssapi/mechglue/g_rel_name.c (gss_release_name): Call
	GSSINT_CHK_LOOP() to validate loopback pointer.

ticket: 4063
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@18417 dc483132-0cff-0310-8789-dd5450dbe970