Fixes many regressions due to commit 3074bd048d08d52874bfa12dafc9a4b365c41a49
(Has to deal with the fact that the event target can be the bug icon
rather than the td tag)
MouseHelper binds this when the callback is added rather than applying it at call time
The icon tag is added when the DOM is built and never removed: the bug icon is
added and removed via its class
Merge branch 'master' of https://github.com/nofatclips/minesweeper.js