2to3: Apply `funcattrs` fixer. Closes #3058.

This replaces the `b.func_xxxx` with newer `__xxxx__` attribute names
For example, `f.__name__`  replaces `f.func_name`
Merge pull request #3059 from charris/2to3-funcattrs

2to3: Apply `funcattrs` fixer. Closes #3058.