Allow multiple indented blocks in REPL by jackoconnordev · Pull Request #6097 · RustPython/RustPython

There aren't any tests but being able to do nested for loops seems like
a pretty big win to me so I'm going to put up for review.

The original returned boolean clearly had **false positives** for
detecting bad errors for things like nested `if` and `for` statements.
What is less clear is if there are any **true positives** which I am no
longer catching with the updated return value.