Fix quirks mode

When `demo.html` page is opened in quirks (or simulated IE7) mode, `jquery.splendid.textchange.js` starts throwing errors. This is because in the above modes `target.constructor` is undefined but code expects it to always have a value.

This pull request makes code using `target.constructor` mode defensive.

Other changes eliminate errors reported by JSLint while still preserving original code formatting.

Tested in IE8 on Windows XP (using ModernIE VM), Chrome and Firefox.