Assignment of runs allowed in boxscore on certain fielder's choice plays.

Corrects an edge case in boxscore generation, on the assignment of runs
scored by trailing runners when a preceding runner has been put out,
on a fielder's choice play.
Adjust handling of backward advances to avoid clobbering runner data.
Update version number to 0.6.3.
Merge branch 'maint'

Conflicts:
	configure.ac