move image guessing function into bpy_extras


git-svn-id: https://svn.blender.org/svnroot/bf-extensions/trunk/py/scripts/addons@4461 96b784f8-4ae3-dd11-aff7-0030488c597c
add option to copy textures on export.


git-svn-id: https://svn.blender.org/svnroot/bf-extensions/trunk/py/scripts/addons@4462 96b784f8-4ae3-dd11-aff7-0030488c597c
Re-added Flip Normals option by request.  Also removed WIP warning.

git-svn-id: https://svn.blender.org/svnroot/bf-extensions/trunk/py/scripts/addons@4463 96b784f8-4ae3-dd11-aff7-0030488c597c