Document disallowed copy and allowed move better.
Document disallowed copy and allowed move better.

Moreover when the deleted function was private, the compilation failed
with (rather cryptic) error that the function is private instead of
noticing that the function is deleted.

MiUishadow/magnum,MiUishadow/magnum,ashimidashajia/magnum,ashimidashajia/magnum,DerThorsten/magnum,MiUishadow/magnum,DerThorsten/magnum,DerThorsten/magnum,DerThorsten/magnum,ashimidashajia/magnum,MiUishadow/magnum,ashimidashajia/magnum,ashimidashajia/magnum,MiUishadow/magnum,DerThorsten/magnum,MiUishadow/magnum