Replicate Vidalia's ability to close arbitrary circuits

The main goal is to enable users to debug potentially buggy or malicious exit nodes. For example, you get an unexpected HTTPS or SSH warning, write down the info about your exit node, and close that circuit to get a fresh one and confirm your suspicions.

• For HTTPS, one can already use Torbutton’s New Identity feature to achieve the same result. IIRC the upcoming Torbutton’s per-tab circuits viewer will have a “New circuit for this tab” feature, that will make it even better.
• For other kinds of connections (ssh, imaps, pop3s, etc.) then there are two ways:
  • either using arm to trigger a New Identity, which is not that crazy: close the software that initiated the connection, open a root terminal (which may be a blocker in itself), run “arm”, type “m”, “down arrow” then “enter”
  • or restarting Tor, e.g. by disconnecting and reconnecting from the network using the NM applet

Also, it would be good if arm directly allowed to close one arbitrary circuit: https://trac.torproject.org/projects/tor/ticket/14979.

Related issues

• Related to #9811 (closed)
• Related to #9001 (closed)
• Related to #11214 (closed)
• Blocked by #8915 (closed)
• Blocked by #6841 (closed)

Original created by @intrigeri on 8927 (Redmine)