Reorder forms for compilability.
Reimplement MAYBE-CLOSES-OVER-P using SB-WALKER.
Register specials in the context.
Update MAYBE-CLOSES-OVER-P call sites.
Remove an obsolete comment.
LET*, LAMBDA: Fix use of MAYBE-CLOSES-OVER-P to also search references from binding forms.
Add special handling for MACROLET, SYMBOL-MACROLET, FLET, LABELS.