Add screenshot to README showing Sparkle in action.
Check for a modal window being onscreen before trying to put up the Sparkle prompt.
Updated changelog
Merge pull request #426 from alfwatt/master

Check for a modal window being onscreen before trying to put up the Spar...
Added SUUpdater delegate method for failures.
Call delegate didAbort in other drivers when showErrors is false.
Merge pull request #432 from yetamrra/master

Add delegate method for errors
Changed a straight apostrophe into a curly one

Changed the apostrophe in the title of the ‘Don’t Check’ button on the update permissions prompt dialog from a straight one to a curly one.
Merge pull request #434 from codyrobbins/master

Changed a straight apostrophe into a curly one