Analyze how long after earning the HSDir flag relays go away

First, extract status entries with the HSDir flag set from the metrics
database:

  tordir=> \o hsdir.csv
  tordir=> SELECT validafter, fingerprint FROM statusentry
           WHERE validafter >= '2010-05-01' AND validafter < '2011-05-01'
           AND ishsdir IS TRUE ORDER BY validafter, fingerprint;
  tordir=> \o

Next, calculate continuous sessions of a relay having the HSDir flag.  For
each such session, extract the fingerprint and the first and last time it
was listed in the network status with the HSDir flag.  Also calculate the
session duration in seconds:

  $ javac EvaluateHsDirs.java && java EvaluateHsDirs

Plot an ECDF of the session length:

  $ R --slave -f hsdir-sessions.R

