When you mean (a=b(c,d)) >= 0, you had better not say (a=b(c,d)>=0).
We did the latter, and so whenever CircPriorityHalflife was in the
consensus, it was treated as having a value of 1 msec (that is,
boolean true).
We need to make sure we have an event_base in dns.c before we call
anything that wants one. Make sure we always have one in dns_reset()
when we're a client. Fixes bug 1341.