settles some of the issues
(a) typeinst/typedecl revamp, (b) now using typedecl/typeinst in context stack, (c) slots are properly instantiated
rearranged message instances in message.nest, cleanup nest, fixed some old references to mode
type_helper: figure out whether we are dealing with a typeinst or a typedecl using llength_args (not a very good way but still...)
regenerated message.out