Duplicate votes on 0.3.4 and later

Tor 0.3.4 changed periodic event timings.

Occasionally, this means authorities send a duplicate vote:

Detail: chutney/tools/warnings.sh /Users/base/chutney/net/nodes.1535124133
Warning: Rejected vote from 127.0.0.1 ("Duplicate discarded"). Number: 1

Maybe we should avoid sending the same vote twice? (Or maybe not, if the remote authority restarts.)