fixed the isValid() method
sadffdsgfdsgfgfdfdsasfds
Merge branch 'master' of https://github.com/eomprogramming/Algebra-Tiles

Conflicts:
	bin/Algebra-Tiles.apk
	bin/classes.dex
	bin/classes/com/eomprogramming/algebratiles/AlgebraTilesActivity$1.class
	bin/classes/com/eomprogramming/algebratiles/AlgebraTilesActivity.class
	bin/classes/com/eomprogramming/algebratiles/datastructure/Stack$ListIterator.class
	bin/classes/com/eomprogramming/algebratiles/datastructure/Stack.class
	bin/classes/com/eomprogramming/algebratiles/math/QEquation.class
	bin/classes/com/eomprogramming/algebratiles/model/Row.class
	bin/classes/com/eomprogramming/algebratiles/model/RowGroup.class
	bin/classes/com/eomprogramming/algebratiles/model/Tile.class
	bin/classes/com/eomprogramming/algebratiles/model/TileLayout.class
	bin/resources.ap_
	src/com/eomprogramming/algebratiles/math/QEquation.java
	src/com/eomprogramming/algebratiles/model/Row.java
	src/com/eomprogramming/algebratiles/model/RowGroup.java
	src/com/eomprogramming/algebratiles/model/Tile.java
FINAL COMMIT (hopefully)