Update of the DDS plugin for ETC1 and for the optional specification of a texture corpession format

This code have been also merged : http://forum.worldwindcentral.com/showthread.php?18819-DDS-Plugin-for-geoserver&p=109343&viewfull=1#post109343

Justification here :
http://forum.worldwindcentral.com/showthread.php?43415-Improve-compatibility-with-non-DDS-compatible-device