Log Message:
Changes 4.7.0:
* Added in memory caching of init file search results for substantial
  acceleration in some application environments (like MapServer).
* Regenerated nad/epsg init file with EPSG 7.1 database, including new
  support for Google Mercator (EPSG:3857).
* Various thread safety improvements, including preliminary support for
  a mutex lock around some operations, like grid loading.