Remove warning message on backwards advance.
Accept review and NDP flags on walks and OA, for December 2014 Retrosheet release.
Implement support for courtesy runners and re-entry.

This back-ports features added in 0.7.0 in commits 2967b08 and
faffe69 to handle correctly the case in which a player re-enters
the game, either in the same or a different lineup slot.
Updated standard distribution files.
Update version number to 0.6.4, copyright dates to include 2014.
Merge branch 'maint'