Make the set type separate from the set-element (linked list node) type

Make the set type separate from the set-element (linked list node) type

* generic/gssapiP_generic.h (g_set): New struct type.
(G_SET_INIT): New macro.
* generic/util_validate.c (g_save, g_validate, g_delete): Change first argument
to take a g_set * rather than void **; use the address of the void pointer from
the structure.
(g_save_name, g_save_cred_id, g_save_ctx_id, g_validate_name,
g_validate_cred_id, g_validate_ctx_id, g_delete_name, g_delete_cred_id,
g_delete_ctx_id): Updated first argument type.
* genericgssapiP_generic.h: Declarations updated.

* krb5/gssapi_krb5.c (kg_vdb): Change type to g_set and initialize.
* krb5/gssapiP_krb5.h (kg_vdb): Declaration updated.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@16166 dc483132-0cff-0310-8789-dd5450dbe970