SI-7345 Doc and TODO comments around Context.
SI-7345 Remove unneeded warning.

According to Hubert, during normal operation we can start buffering
errors in a context with existing errors. So the warning would be noisy.
SI-7345 Factor out method to clear and restore undetparams.

Also refactored `handleOverloaded` to avoid use of a mutable Buffer
SI-7345 Drive by refactoring of pattern matching for `arg: _*`.