Don't generate symbols that shadow built-ins

[mehaase]

For example, there's a CDP domain called "Input" that gets Pythonified to input. If you import this domain, it will shadow the built-in input() function, which is poor style.

We can probably use the builtins module to identify such symbol names, and then typical Python style is to append an underscore, so input.insert_text(...) would become input_.insert_text(...).