make clean breaks virtualenvs stored inside the repo clone

[godlygeek]

If you create a virtualenv inside a clone of the repo, running make clean will break it by removing all of the *.so files inside of it. We should improve our make clean to only remove files that we know we've created.

[Helithumper]

I believe this could be fixed with just a find . -not -path $VIRTUAL_ENV in the first line of the clean target, however would there be another case where there may be files we would not want to clean up?

[godlygeek]

It's a bit trickier than that, since you might have multiple virtualenvs all in the same repo root. What you're proposing would stop it from breaking the active virtualenv, but wouldn't stop it from breaking deactivated ones.

The safer option is enumerating the files that we expect to be created by commands in the makefile, and only removing those, rather than using a recursive wildcard.

[jayybhatt]

I'll take this