Correctly destroy: wait for closeMenus()
Remove <popupset> even if onDestroy() failed
Better work without Custom Buttons
And additional feature: should work from "code" section too (better now)

Based on code from Toggle Restartless Add-ons
https://github.com/Infocatcher/Custom_Buttons/commit/a025caa3ec9c93a18a6c665b6a5509c2cffcab19
Fix typo: correctly call onDestroy()
Correctly detect button: ignore <popupset>
For https://github.com/Infocatcher/Custom_Buttons/blob/master/Extensions_Developer_Tools/extDevToolsMouseGesturesLauncher.js
Bump version to 0.1.0 - 2013-02-02