tor 0.2.4.20

"fixes an issue that would create more preemptive circuits than actually need, and a security issue related to poor random number generation."

* Announcement: https://lists.torproject.org/pipermail/tor-talk/2013-December/031483.html

Closes #25764.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>