Improve locality->street segment queries
Improve locality->street segment queries

For a reasonably large locality, such as California's L.A. County with
~467,000 street segments, this bring the runtime _of the query alone_
from 13.5 seconds down to 3.5 seconds (when combined with appropriate
indexes for the dataset.) For the extra curious, compare the query plans
generated by running `explain analyze`

votinginfoproject/Metis,votinginfoproject/Metis,votinginfoproject/Metis