Fixes being able to place multiple fulltile window on a grille.
Fixes being able to place a fulltile window on a grille with single dir windows.
Fixes a typo in grille message.
Grille now needs to be anchored to place a window on it.
Merge pull request #6187 from phil235/GrilleWindowFix

Fixes being able to place multiple fulltile window on a grille.