Fix disassembling closures.

When looking for the function information GET-FUN-SEGMENTS used
%SIMPLE-FUN-NAME to match the name, but closures are not simple funs.
Get a simple fun before calling %simple-fun-name.
Properly destructure WITH in LOOP.

When transforming LOOP destructuring into DESTRUCTURING-BIND each
sublist should start with &optional.

Reported by Robert Strandh.