Background being unloaded by Chrome due to inactivity

[luciopaiva]

This is "issue 1" as referred to by the discussion in #30. Google Chrome can unload the background page on its own will and the extension must be programmed to handle it properly. As it is now, Witchcraft can fail if the user opens the pop-up window when the background page is marked as "inactive" by Chrome.

Reference: https://stackoverflow.com/a/26073197/778272