o Minor bugfixes:
   - Simplify the logic that causes us to decide if the network is unavailable
     for purposes of recording circuit build times. If we receive no cells
     whatsoever for the entire duration of a circuit's full measured lifetime,
     the network is probably down. This should hopefully reduce some of the
     cases where we see ridiculous circuit build timeouts for people with spotty
     wireless connections. Fixes bug 1772; bugfix on 0.2.2.2-alpha.
   - Prevent the circuit build timeout from becoming larger than the maximum
     build time we have ever seen. Also, prevent the measurement time period
     from becoming larger than twice that value. Fixes bug 1772; bugfix on
     0.2.2.2-alpha