From Alexander Sinditskiy, "My changes added support for gltexstorrage2d for texture2d.

Initially I described issue in message:
http://forum.openscenegraph.org/viewtopic.php?t=13820
It solves issue with compiling texture using ico from image with mipmaps

I added enviroment variable OSG_GL_TEXTURE_STORAGE_ENABLE to control usage of glTexStorage2d. Initially it is disabled.

It used only if image have mipmaps.

Another issue is converting from internalFormat + type to sized internal format. I created sizedInternalFormats[] struct where sized internal formats are ordered from worse->best.
also this struct have commented lines. Commented formats are listed in
http://www.opengl.org/wiki/GLAPI/glTexStorage2D
but looks like not using in osg."

Note from Robert Osfield.  Changed the env var control to OSG_GL_TEXTURE_STORAGE and made it's value true by default when the feature is supported by the OpenGL driver.  To disable to
use of glTexStorage2D use OSG_GL_TEXTURE_STORAGE="OFF" or "DISABLE"



git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14275 16af8721-9629-0410-8352-f15c8da7e697
changed debug message to use OSG_DEBUG


git-svn-id: http://svn.openscenegraph.org/osg/OpenSceneGraph/trunk@14276 16af8721-9629-0410-8352-f15c8da7e697