Add validation to ensure we don't mv a file onto itself

Fixes #831
Update changelog with bugfix
Merge branch 's3-mv-same' into develop

* s3-mv-same:
  Update changelog with bugfix
  Add validation to ensure we don't mv a file onto itself
Fix changelog entry for merge of #831

This is not in the 1.3.21 release, it will be part
of the next release.