Added new random mode for sampling of sign flips

Above 53 scans the binary-coding fails as Matlab’s double’s significand
runs out of precision.  Ideally a random subset method would be used,
i.e. I’d check to see that PiCond has no duplicates… but that’s too
much of a pain right now.  To do (or not).
Merge branch 'SnPM13'

Mering local changes; now OneSampleT handles more than 53 subjects

Fixed problem (due to finite floating point precision) with nScan>53