Implied arg split not working as expected

[jaraco]

I've noticed that the pip-run script.py mode isn't working as intended. It fails when it tries to install the requirement script.py, but since script.py is an existent file in the current directory, I'd expect it to infer the usage and treat it as pip-run script.py.

[jaraco]

The use of split_before didn't have the intended effect... because it doesn't actually perform a split if the first element matches the predicate, making the results indistinguishable on the first element:

 pip-run main $ pip-run more-itertools -- -q
>>> from more_itertools import split_before
>>> list(split_before([1, 0], pred=bool))
[[1, 0]]
>>> list(split_before([0, 0], pred=bool))
[[0, 0]]
>>> list(split_before([0], pred=bool))
[[0]]
>>> list(split_before([1], pred=bool))
[[1]]