doc: licensing cleanups

doc: licensing cleanups
Use nice utf-8 © instead of "(c)". Remove licensing statements on utility modules that have been assigned to allmydata.com by their original authors. (Nattraverso was not assigned to allmydata.com -- it was LGPL'ed -- but I checked and src/allmydata/util/iputil.py was completely rewritten and doesn't contain any line of code from nattraverso.)  Add notes to misc/debian/copyright about licensing on files that aren't just allmydata.com-licensed.