By: Mark Barber The Oscar-nominated doc Glen Campbell: I’ll Be Me follows the title legendary country singer through both his final tour and his struggle with Alzheimer’s disease.  Necessarily poignant (if artificial) and urgent about the subject and his inevitably fatal illness, the film still occasionally struggles with the presence of exploitation. Numerous interviews with family, friends, and celebrities set up a touching rumination on the ineluctable flow of time.  But the oft-witty Campbell serves…