Make sure we don't hear back from replies after we've cleared them.
Improved rotation computation.
Basic sharing of the avatar voxel URLs.
Don't restart the download when we're given the same URL.
Fix for URL decoding.
Merge pull request #489 from ey6es/master

Voxel URL sharing between avatars, tweak to rotation computations, fix for null replies.
Merge branch 'master' of https://github.com/worklist/hifi