Better error messages in case of typecheck errors.

Now closure implementaion and closure reference are represented as tobjectdef with flag isClosure. To make nice error messages I hardcoded into few places printing of "reference to procedure" instead of class name. Better to refactor this in the future.
Allow to call closure-variable using procvar(arg1, arg2, arg3, ...) or procvar; syntax. Fix error messages. Add more tests.