2 - Path Use Bias: Perform separate accounting for successful circuit use.
3 Separate statistics on stream attempt versus success rates are kept
4 for each guard. Configurable thresholds are provided to determine
5 when to emit log messages or disable use of guards that fail too
8 - Remove a source of rounding error during path bias count scaling.
9 - Don't count cannibalized circuits as used for path bias until we
10 actually try to use them.
11 - Fix circuit_package_relay_cell warning message about n_chan==NULL.