OpenEXR decoder

Additional fixes and enhancements by Vittorio Giovara, Gonzalo Garramuno,
Nicolas George, Paul B Mahol and Michael Niedermayer.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
fate: add exr tests

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
codec_desc: set lossless attribute for SGI and DPX
sgi: K&R formatting cosmetics
sgi: check maximum supported resolution

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
sgi: fix end of line boundary detection
sgi: set the row boundary to the correct value
sgi: remove redundant argument from read_uncompressed_sgi()
sgi: decode images with 4 channels at 8 and 16 bits
sgi: encode images with 4 channels at 8 and 16 bits
sgi: decode 16bit RLE images
fate: add SGI tests