fix: relative threshold requires global calc.

As in SPM, when relative thresholding is set, then global calculation
(user defined or mean) must be computed.

Before this fix, relative threshold would in fact be absolute threshold
unless global calculation was specified explicitely.
test: unbalanced group in two-sample tests
fix: unbalanced group in two-sample tests
SnPM version updated to 13.0.11
Typo
test: one sample no ext same results as nominal
fix: two-sample two conditions unbalanced
merge SnPM13