Infinite loop in after NS_ERROR_DOM_QUOTA_REACHED

[kpturner]

Scenario.

• localStorage already has other data in it.
• Plug-in tries to store json, but it is too big.
• cleanUpLocalStorage has a go at cleaning up but finds nothing to do (the data already in localStorage has nothing to do with the plug-in)
• Loops around and tries again. Still too big (obviously). Loops around and tries again......and so on.

Result: Infinite loop.

[stephen-uac]

My fix here should resolve this issue:

#10