supposed to support 10.8+ but no longer builds on 10.9

[RJVB]

several small things sneaked in that make it impossible to build the code on 10.9 :

• use of something called "box control" in Preferences.xib (required Xcode >= 7)
• a new NSTextField property (alignment)
• a new NSMenuItem property (isSeparatorItem; use the regular @selector instead)