Recover better from TCP connections to Tor servers that are broken but

don't tell you (it happens!); and rotate TLS connections once a week.

1) If an OR conn becomes more than a week old, make it obsolete.
2) If it's obsolete and empty, kill it.
3) When an OR makes a second connection to you, allow it.
4) If we want to send a new create cell, but the best conn we've
   got is obsolete, and the router is 0.1.1.9-alpha-cvs or later, ask
   for a new conn instead.
5) When we time out on circuit building on the first hop, make that
   connection obsolete.


svn:r5429