git-annex 0.17 released with [[!toggle text="these changes"]]
[[!toggleable text="""
   * unannex: Now skips files whose content is not present, rather than
     it being an error.
   * New migrate subcommand can be used to switch files to using a different
     backend, safely and with no duplication of content.
   * bugfix: Fix crash caused by empty key name. (Thanks Henrik for reporting.)"""]]