Fix bug when parsing bwhist with unexpected Interval

Fix bug when parsing bwhist with unexpected Interval

Previously, our state parsing code would fail to parse a bwhist
correctly if the Interval was anything other than the default
hardcoded 15 minutes.  This change makes the parsing less incorrect,
though the resulting history array might get strange values in it if
the intervals don't match the one we're using.  (That is, if stuff was
generated in 15 minute intervals, and we read it into an array that
expects 30 minute intervals, we're fine, since values can be combined
pairwise.  But if we generate data at 30 minute intervals and read it
into 15 minute intervals, alternating buckets will be empty.)

Bugfix on 0.1.1.11-alpha.