Faster Simd

On maxwell compress1 and compress2 can be run in one run instead of two.(750TI + 20KHASH)
stratum: add more checks on request id
stratum: difficulty can be buggy with values close to zero

bug seen on windows with xpool.ca (x11)
Update jansson windows sources to 2.6

There was sometimes problems with float values close to 0 (like 0.001)