objclosure: Fix printing of generator closures.

The code previously assumed that only functions can be closed over.
stream: Return errno value as first arg of OSError exception.

This is CPython-compatible convention established yet in acb13886fc837a1bb9.
stream: Handle non-blocking errors in readline() properly.

Just like they handled in other read*(). Note that behavior of readline()
in case there's no data when it's called is underspecified in Python lib
spec, implemented to behave as read() - return None.
modure: Update to re1.5 v0.6.1, fixed and extended character class support.