T1 flag optimizations (#172)

[rouault]

This patch set consists in :

• porting Carl Hetherington T1 patch that optimimzed encoder side
• fix/implement VSC encoding in it
• adapt C. Hetherington tricks to the decoder side
• use macros in MQC decoding and sig/ref/cleanpass for better assembly generation

Results on the performance test suite (ref time is current master):

../../data/input/nonregression/kodak_2layers_lrcp.j2c, 3 iterations, 1 threads, DECOMPRESS: ref_time 2226 ms, new_time 1967 ms, (improvement) -11.6 %
../../data/input/nonregression/kodak_2layers_lrcp.j2c, 5 iterations, 2 threads, DECOMPRESS: ref_time 3019 ms, new_time 2781 ms, (improvement) -7.9 %
../../data/input/nonregression/kodak_2layers_lrcp.j2c, 10 iterations, 4 threads, DECOMPRESS: ref_time 4864 ms, new_time 4548 ms, (improvement) -6.5 %
../../data/input/conformance/p0_07.j2k, 3 iterations, 1 threads, DECOMPRESS: ref_time 5647 ms, new_time 4959 ms, (improvement) -12.2 %
../../data/input/conformance/p0_04.j2k, 10 iterations, 1 threads, DECOMPRESS: ref_time 703 ms, new_time 622 ms, (improvement) -11.5 %
../../data/input/nonregression/X_4_2K_24_185_CBR_WB_000.tif, 3 iterations, 1 threads, COMPRESS: ref_time 6588 ms, new_time 5291 ms, (improvement) -19.7 %
TOTAL: ref_time 23049 ms, new_time 20172 ms, (improvement) -12.5 %

On (private image) MAPA.jp2 (recoded with standard flags), decoding time goes from 50.168 s to 45.030, so a reduction by 10% of decoding time as wel.

[rouault]

Has been merged into master.