Running with --pdb seems to prevent recognizing changes

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I'm having some issues triggering a restart on changes while a test is running.

I've isolated the factor to using ptw -- --pdb

Do others see consistent behavior? I'm on the latest release. I realize that's not a lot of information - let me know what else would be helpful.

(NB: I'd argue that passing --pdb as a pytest arg ideally wouldn't affect ptw at all ref #89)

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This may be due to the wait argument implicit in pdb?

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Would you take a PR to adjust the --pdb change to only affect ptw's behavior if a ptw argument, rather than a pytest argument? With the associated documentation