Replace AppleScript in MacOsX#enable!

[hartmantis]

Ideally, this would be calling a resource in the mac_os_x cookbook (much like the auto_run resource in the windows cookbook), but that's complicated by:

• Doing it in AppleScript is easy and works, but requires that a user be logged into OS X.
• defaults can be used to write to ~/Library/Preferences/com.apple.loginitems.plist, but it initially doesn't exist and all and has a weird structure once it is generated.