Add changelog for this branch.

changes/cbt-bugfixes

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+ o Major bugfixes:
+   - Ignore negative and large timeout values that can happen during a
+     suspend or hibernate. These values caused various asserts to fire
+     in the circuit build times code, crashing Tor. Bug 1245, bugfix on
+     0.2.2.2-alpha.
+   - Alter calculation of Pareto distribution parameter 'Xm' for Circuit Build
+     Timeout learning to use the weighted average of the top N=3 modes. This
+     should improve the timeout calculation in some cases, and prevent
+     extremely high timeout values. Bug 1335, bugfix on 0.2.2.2-alpha.
+   - Implement a filtering step to recompute synthetic build times every time
+     the timeout changes. Additionally, place a lower cap on synthetic build
+     times, and allow this cap to be controlled by the consensus. This should
+     also improve the build time calculations, and should eliminate a case
+     where Tor was allocating an excessive amount of temporary memory during
+     timeout calculation. Bugs 1335 and 1245, bugfix on 0.2.2.2-alpha.
+
+ o Minor bugfixes:
+   - Eliminate a case where a circuit build time warning was displayed after
+     network connectivity resumed.
+
+ o Minor features:
+   - Add a TIMEOUT_RATE keyword to the BUILDTIMEOUT_SET control port event,
+     to give information on the current rate of circuit timeouts over our
+     stored history.
+   - Add ability to disable circuit build time learning via consensus
+     parameter and via a LearnCircuitBuildTimeout config option. Also
+     automatically disable circuit build time calculation if we are either
+     a AuthoritativeDirectory, or if we fail to write our state file. Bug 1296.
+
+