2.4.0

• geoipupdate now checks that the database directory is writable. If it
  is not, it reports the problem and aborts.
• geoipupdate now acquires a lock when starting up to ensure only one
  instance may run at a time. A new option, LockFile, exists to set the
  file to use as a lock. By default, LockFile is the file
  .geoipupdate.lock in the database directory.
• geoipupdate now prints out additional information from the server when
  a download request results in something other than HTTP status 2xx. This
  provides more information when the API does not respond with a database
  file. In conjunction with changes to the download service itself, errors
  such as lacking a subscription no longer show up with the message "not a
  valid gzip file".
• ${datarootdir}/GeoIP is now created on make install. Reported by Antonios
  Karagiannis. GitHub #29.
• Previously, a variable named ERROR was used. This caused issues building
  on Windows. Reported by Gisle Vanem. GitHub #36.