tor 0.2.4.21 and 0.2.5.2-alpha

"Tor 0.2.4.21 further improves security against potential adversaries who
find breaking 1024-bit crypto doable, and backports several stability
and robustness patches from the 0.2.5 branch."

* 0.2.4.21: https://lists.torproject.org/pipermail/tor-talk/2014-March/032242.html
* 0.2.5.2-alpha: https://lists.torproject.org/pipermail/tor-talk/2014-February/032150.html