This adds a opj_set_decoded_components(opj_codec_t *p_codec,
OPJ_UINT32 numcomps, const OPJ_UINT32* comps_indices) function,
and equivalent "opj_decompress -c compno[,compno]*" option.
When specified, neither the MCT transform nor JP2 channel transformations
will be applied.
Tests added for various combinations of whole image vs tiled-based decoding,
full or reduced resolution, use of decode area or not.