I'm not sure about prior versions, but with Xcode 6.1 and Yosemite (OS X 10.10) two commands are actually required to disable anti-aliasing locally in Xcode.
First, as has already been stated, you need to enter the following at a terminal console:
defaults write com.apple.dt.Xcode NSFontDefaultScreenFontSubstitutionEnabled -bool YES
Then, secondly:
defaults write com.apple.dt.Xcode AppleAntiAliasingThreshold <some integer value>
This is preferable to disabling font smoothing or antialiasing throughout the entire operating system.
It should really be an option to check/uncheck inside the program itself, but at least this works.