for signed under certain conditions (no tiling or resolution reduction)

This reverts commit 77eb9b4256fd6b5738b780b55f4b7f55c43e1adf.

and also don't set gamma if there is an ICC profile

is wrong for all tiles after the first when decoding multiple tiles, if
cmap/pclr/cdef boxes are present in jp2 file

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