Add pylintrc and improve depslint.py correctness and stylictic coherence...

You may not like the stylistic changes. Feel free to refuse them.

I didn't touch depstrace.py since I'm basically rewritting it eventually.

....

pylintrc found a few bugs in it like:
- using a mutable instance like [] as a default argument value
- invalid number of arguments
- builtin aliasing
- unnecessary global statement
- unreferenced variables, while not strictly a bug, it's confusing.

In addition, make spacing 2 lines between file level symbols and move main code
into a main() function to fix potential scoping issues.