pdb: handle quitting in post_mortem

[blueyed]

help quit in pdb says:

Quit from the debugger. The program being executed is aborted.

But pytest would continue with the next tests, often making it necessary
to kill the pytest process when using --pdb and trying to cancel the
tests using KeyboardInterrupt / Ctrl-C.

TODO:

• changelog
• test?

[nicoddemus]

Thanks! We also need a test and a CHANGELOG entry. 👍

Done news/tests

[blueyed]

py3 displays it as "_pytest.outcomes.Exit: Quitting debugger", while py2 uses Exit: Quitting debugger.
Is this OK?

[nicoddemus]

I think so, we can improve this later if need be

[blueyed]

I need to touch it anyway again, so might as well add a __repr__ or somethng for Exit.

That's likely not it though, so will just adjust/losen the test in this regard.

[nicoddemus]

Sounds good, thanks!

[coveralls]

Coverage increased (+0.01%) to 93.791% when pulling 86c7dcf on blueyed:pdb-quit into 27d2683 on pytest-dev:master.