Migrating from a URL key to an MD5E key (after addurl --fast using an external special remote) fails:

    (master_env_py27_v28) [03:15 PM /data/ilya-work]$ git annex --verbose --debug migrate A4.taxfilt.bam
    [2018-10-29 15:15:55.197015] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-files","--cached","-z","--","A4.taxfilt.bam"]
    [2018-10-29 15:15:55.232756] chat: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","check-attr","-z","--stdin","annex.backend","annex.numcopies","annex.largefiles","--"]
    [2018-10-29 15:15:55.232934] read: git ["--version"]
    [2018-10-29 15:15:55.233841] process done ExitSuccess
    migrate A4.taxfilt.bam failed
    [2018-10-29 15:15:55.263931] process done ExitSuccess
    git-annex: migrate: 1 failed
    (master_env_py27_v28) [03:15 PM /data/ilya-work]$ git annex info A4.taxfilt.bam
    file: A4.taxfilt.bam
    size: 12.75 megabytes
    key: URL-s12750247--dx://file-FJZjKx800YQPJ5j589Q2Kfzv/A4.taxfilt.bam
    present: true
    (master_env_py27_v28) [03:16 PM /data/ilya-work]$ git annex whereis A4.taxfilt.bam
    whereis A4.taxfilt.bam (2 copies)
            0928dfcc-4dbe-4c24-a5a0-ac05c4a2c829 -- ilyas_main_repo [here]
            6803648c-87e6-41ef-9570-48adb13ff59a -- [mydx]
    
      mydx: dx://file-FJZjKx800YQPJ5j589Q2Kfzv/A4.taxfilt.bam
    ok
    (master_env_py27_v28) [03:16 PM /data/ilya-work]$ git annex --verbose --debug migrate A4.taxfilt.bam --backend MD5E
    [2018-10-29 15:17:15.621264] read: git ["--git-dir=.git","--work-tree=.","--literal-pathspecs","ls-files","--cached","-z","--","A4.taxfilt.bam"]
    migrate A4.taxfilt.bam failed
    git-annex: migrate: 1 failed

> [[fixed|done]] --[[Joey]]
