Fix #31338: python enum properties can now specify icons for items, in the following
order: (identifier, name, description, icon, unique number)

This also works without the icon still, for compatibility.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54055 954f8c5b-7b00-dc11-b283-0030488c597c