Log Message:
Update to 8.1.

Upstream does not provide a NEWS file, but says of 8.1:

  Version 8.1 of the EPSG Geodetic Parameter Dataset comprises of data
  corrections and updates to the v8.0 release of August 2012.

  Changes as documented in Change Records through 2012.093, but with
  actions still remaining on some change requests.

  New data for Brazil, Tonga and the Arctic.

  Significant revisions to data for Brunei and Mayotte.

  Minor revisions to data for Europe, former Soviet Union and New Zealand.