PAtch for optical sensors from Emmanuel

[gpotts]

Here is a patch for the optical sensors: mostly access to metadata required for radiometric calibration. I'm not sure when I last send you our modification on the optical sensor: it's better to refer to the files rather than the patch. I might have missed some files with modifications so it is better to attempt a compilation after applying this one. Same as the previous one: the modification since ossim revision 17734 won't be in those files.

Let me know once it is on the ossim svn, I'll run a diff from home to make sure that nothing is missing.