Add option to return back to the previous circuit
Okay, so I tried to visit some website and got suspicious - encrypted connections were timing out, or I saw something weird on plaintext ones. I retried on new circuit to check, and everything went back to normal. Now I want my previous exit to check it further and report to bad-relays as needed aaand... nobody knows what it was. Tor probably haven't closed old circuit yet, but TBB no longer uses it. From torbutton/components/domain-isolator.js it seems to be impossible to recover old circuit isolator, so should we use @yawning idea from #19206 (closed) of setting it to nonce:counter? Then it would become possible to jump back to old circuit.