1) compare_images when reading a TIFF
2) opj_decompress when writing to a non-TIFF format

decoding to TIFF format, since TIFF will store the profile in a tag.

fixes issue #38 : support force-RGB when applying ICC profile, otherwise output grayscale to grayscale.

Since conformance tests use force-RGB flag, these test continue to work.

2. removed two compatibility structure members

useful for trouble shooting failed ctest cases