Need a better parser/compile error message for mis-placed bindings/assignments

[b1conrad]

KRL doesn't allow name/value bindings except in a prelude or in a function definition. When these are tried in other places, the error messages are unclear/misleading and sometimes don't fail until JavaScript compilation. Need specific examples. But, see also, issue #528, which makes a case for such bindings in an every action block.

KRL doesn't allow entity variable assignments anywhere but in a postlude. When one is attempted in a defaction the error message seen is "ParseError: Expected '('" which is not helpful.