By: Mark Glennon*   I’ll ask a leading authority on Illinois’ single subject rule about it and the “grand bargain” budget solution under discussion in Springfield, but first a little background.   The single-subject clause of the Illinois Constitution is in Article I, § 8(d), paragraph 2. It provides:   Bills, except bills for appropriations and for codification, revision or rearrangement of laws, shall be confined to one subject. Appropriation bills shall be limited to the subject of appropriations.   But the grand bargain is a gigantic cornucopia of different subjects. It addresses pension reform, workers’ compensation, security for