Update to 2.5.0

Also, create PREFIX/share/GeoIP, as it's needed with the default
configuration.

Note that conf option names have changed with this release, but the
old names will continue to work.

• Replace use of strnlen() due to lack of universal availability. First reported by Bill Cole. GitHub issue #71.
• Document the LockFile option in the GeoIP.conf man page. GitHub issue #64.
• Remove unused base64 library. PR by Mikhail Teterin. GitHub PR #68.
• Add the new configuration option PreserveFileTimes. If set, the downloaded files will get the same modification times as their original on the server. Default is 0 (unset). PR by Rainer Jung. GitHub PR #63.
• Use the correct types when calling curl_easy_setopt(). This fixes warnings generated by libcurl's typecheck-gcc.h. PR by Michael Kaufmann. GitHub PR #61.
• In GeoIP.conf, the UserId option was renamed to AccountID and the ProductIds option was renamed to EditionIDs. The old options will continue to work, but upgrading to the new names is recommended for forward compatibility.