bug#20817: 25.0.50; Problems with upgrading of packages

[Mark Karpov]

> Your melpa address is outdated. Try changing it to melpa.org/packages

I didn't know that. I've refreshed the address, but the error message
doesn't go away (from *Messages* buffer):

  Thursday, 18 June 2015
  Importing package-keyring.gpg...done
  Package refresh done
  6 packages can be upgraded; type `U' to mark them for upgrading.
  error in process filter: peculiar error: 404 [2 times]

I still cannot upgrade anything, because it says that packages are
unavailable.