Fix two bugs in multiclosure code:

Fix two bugs in multiclosure code:

- non-canonical multi-closure entries appearing in letrecs were
computed incorrectly.  The context offset is not the context after
binding since the code has not finished pushing.

- referencing a closure from within itself cannot bypass the variable
lookup code if the closure for environment is not the closure for
value.  This only affects machines where closures are canonicalized
for environment.