Imbuf types refactor.

ImBuf types were getting stored as bitflags in a 32bit integer which had
    already run out of space. Solved the problem by separating file type to
    an ftype enum, and file specific options to foptions.

    Reviewed by Campbell, thanks a lot!

source/blender/imbuf/intern/oiio/openimageio_api.cpp

@@ -268,7 +268,7 @@ struct ImBuf *imb_load_photoshop(const char *filename, int flags, char colorspac
 		return NULL;
 
 	/* ImBuf always needs 4 channels */
-	ibuf->ftype = PSD;
+	ibuf->ftype = IMB_FTYPE_PSD;
 	ibuf->channels = 4;
 	ibuf->planes = (3 + (is_alpha ? 1 : 0)) * 4 << basesize;