LABELS, FLET: Add implicit block to function definitions.
PREPARE-FORM: Make the context argument mandatory.
LAMBDA: Handle dynamically bound &REST arguments correctly.
LAMBDA: Process &REST before &KEY and &AUX.
LAMBDA: Don't spuriously error out on non-KEYWORDP keyword arguments.
LAMBDA: Do not generate spurious extra gensym'd variables for &AUX bindings.