Add a tmp/test.pid file so two test processes can't run simultaneously

[sam]

Right now you can run bin/doubleshot test twice if you forgot about another open shell already running it. We should warn & exit.

[sam]

Right. Maybe Pathname("/tmp") then? Or a dotfile at-least? Pathname(".doubleshot_test.pid") (which is the same as what you've got, just a dotfile).

I dunno, just not in love with the idea of it dropping a pidfile in plain sight for git to pickup ya know?

[ckrailo]

Done.

[sam]

Thanks. Merged.