[RFC] Added forward compatibility aliases for #8175

Is this something we want?

After renaming some constants in #8175, it became harder to write the
same code to target 0.3.x and 0.4-dev. This PR potentially adds aliases,
so that when 0.3.1 gets released, less mainanance intrested package
authors can drop support for 0.3.0, and be compatible with both 0.3.1
and 0.4-dev with the same code base, without version conditionals.

I have tried to fix the `split`/`rsplit` functions in the same way, but it was somewhat tricky, so I wanted to ask whether it was wanted first.