Blender Git Loki

Hopefully fixed bug #5437, sculpt - seam selection flushing eats lots of ram on low multires level

This appears to have been caused by the excessive amount of memory that multires was eating up every time an edit operation pushed a new undo copy. Added a hack for multires that allows it to use the same multires data for multiple undo copies until the user actually changes levels (which is when multires data is actually updated.)