Fixed bug preventing compilation without the 10.7 SDK installed

- macosx10.7 was specified as the base sdk, preventing compilation on reasonably new systems

(#313, #306, #283, #279)
Fixed compilation error caused by not using format string

- Using a format string for the last argument to [NSAlert alertWithMessageText:defaultButton:alternateButton:otherButton:informativeTextWithFormat:]

(#313, #298)