Incorrect missed-branch message with return/finally/if

[nedbat]

Describe the bug
In the scriv coverage results, I see this:

The message says the return on 165 wasn't executed, but it is clearly marked as executed. The message should say, "Line 167 didn't return because the condition on 167 was always true."

To Reproduce

1. Check out the scriv repo: https://github.com/nedbat/scriv
2. Install the requirements: make requirements
3. Run tox: tox
4. Open the HTML report in htmlcov/index.html, navigate to the end of src/scriv/format_rst.py

[nedbat]

Now it says "line 6 didn't jump to the function exit" which is vague but not inaccurate. Test added in commit 9b1ab97.