Fix py --apply to work with functions with keyword-only arguments

[asmeurer]

Fixes #226 (PyInf#9140)

[codecov-commenter]

Codecov Report

Base: 72.59% // Head: 72.70% // Increases project coverage by +0.11% :tada:

Coverage data is based on head (b8a30c8) compared to base (0d82450). Patch coverage: 95.74% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #227 +/- ## ========================================== + Coverage 72.59% 72.70% +0.11% ========================================== Files 25 25 Lines 7988 8028 +40 ========================================== + Hits 5799 5837 +38 - Misses 2189 2191 +2 ``` | [Impacted Files](https://codecov.io/gh/deshaw/pyflyby/pull/227?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deshaw) | Coverage Δ | | |---|---|---| | [lib/python/pyflyby/\_py.py](https://codecov.io/gh/deshaw/pyflyby/pull/227/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deshaw#diff-bGliL3B5dGhvbi9weWZseWJ5L19weS5weQ==) | `80.44% <95.74%> (+0.55%)` | :arrow_up: | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deshaw). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=deshaw)

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[aktech]

@dshivashankar1994 The comment has been addressed and have added a test for the same, is it good to merge?