Tor clients won't build paths on testing tor network with no guards or exits

Starting in 0.2.4.10-alpha, with our changes to the minimal requirements for building circuits, clients never consider themselves to be ready to build paths if they're running on a testing tor network without bandwidth info.

Instead they say:

Mar 18 12:00:21.000 [notice] I learned some more directory information, but not enough to build a circuit: We need more descriptors: we have 8/8, and can only build 0% of likely paths. (We have 0% of guards bw, 100% of midpoint bw, and 0% of exit bw.)

Found with Chutney.