2 - Report bootstrapping progress correctly when we're downloading
3 microdescriptors. We had updated our "do we have enough microdescs
4 to begin building circuits?" logic most recently in 0.2.4.10-alpha
5 (see bug 5956), but we left the bootstrap status event logic at
6 "how far through getting 1/4 of them are we?" Fixes bug 9958;
7 bugfix on 0.2.2.36, which is where they diverged (see bug 5343).