Add ETC1 compression format support to DDS driver

From: nicolas <nicolas@nicolas-desktop.(none)>

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27497 f0d54148-0727-0410-94bb-9a71ac55c965
header correction for worldwind client

From: nicastel <nic.castel@gmail.com>

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27498 f0d54148-0727-0410-94bb-9a71ac55c965