The txt files provided (mark-short.txt and explore-short.txt) allow you to 
solve mine3.txt to an EndGame state from a click on the upper righthand 
corner.  To test this, you need to change the 3rd strategy from 
DeriveRuleMineStrategy to PrecomputedMineStrategy.  

At some point in the future, I'll have a larger database of precomputed 
moves available.

Instead of using a HashMap (mapping a MineWindow to {MARK,EXPLORE,UNKNOWN})
I decided instead to use two HashSets, a markSet and an exploreSet.  Both 
the HashMap and the HashSet rely on MineWindow to define a hashCode that
behaves according to the .equals.