krb5: Improve cccol sub naming; add gss_store_cred_into2()

- Formalize the TYPE:collection_name:subsidiary_name naming scheme for
   ccaches in ccache collections
    - KEYRING: ccaches are weird because they have one more optional field: the
      "anchor", so rather than just assume a naming convention everywhere, we
      add new functions as well
 - Add krb5_cc_{resolve,default}_sub() that allows one to specify a
   "subsidiary" ccache name in a collection separately from the
   collection name
 - Add krb5_cc_{resolve,default}_for() which take a principal name,
   unparse it, and use it as the subsidiary ccache name (with colons
   replaced)
 - Make kinit use the new interfaces
 - Add missing DIR ccache iteration functionality
 - Revamps test_cc
 - Add krb5_cc_get_collection() and krb5_cc_get_subsidiary()
 - Bump the ccops SPI version number
 - Add gss_store_cred_into2()
 - Make MEMORY:anonymous not linked into the global MEMORY ccache
   collection, and uses this for delegated cred handles

TBD:

 - Split this up into a krb5 change and gss mech_krb5 change?
 - Add krb5_cc_init_and_store() utility, per Greg's suggestion?

lib/gssapi/krb5/external.c

@@ -404,6 +404,7 @@ static gssapi_mech_interface_desc krb5_mech = {
     NULL, /* gm_query_mechanism_info */
     NULL, /* gm_query_meta_data */
     NULL, /* gm_exchange_meta_data */
+    _gsskrb5_store_cred_into2,
     NULL  /* gm_compat */
 };