These will be used to track if Enumeration's custom data or active state
is overridden on a project.  An overridden Enumeration is one that is associated
with a parent Enumeration.

  #4077

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2947 e93f8b46-1217-0410-a6f0-8f06a7374b81