• write annotation @NonNls to source file;
• invoke 'Add annotations.jar to classpath' quickfix;
• select 'Copy to';
• invoke 'Select Path' and navigate to project directory;
• create a new directory 'lib';
• select 'Yes' to add the new directory to VCS;
• select 'OK' to add annotations.jar to the newly created directory;
  -> annotations.jar is listed as unversioned file.

I'm expecting that IDEA asks me whether I want to add annotations.jar to VCS or not.