Add support for new flags in Retrosheet summer 2013 release.

These changes add support for new flags which appear for the first
time as of Retrosheet's summer 2013 release.  In all cases, it is
a matter of accepting the flags silently; no output fields are affected
by their presence.
Remove batted ball types from bunt strikeouts.

Plays which were coded as strikeouts on bunts previously generated a
batted ball type.  This matched the former behavior of BEVENT.
With the April 2013 version, strikeouts no longer generated batted
ball types; this revision brings cwevent into line.  This would seem
to be a sensible change in the interpretation of the batted ball
type output field.