makes compression a bit less good,
hence a bit more comparable with real text (though still too easy to compress).
level 6 is now stronger than level 4, by a hair.
However, there is still a ratio dip at level 5.
this generator replaces the statistical generator
for the general case when no statistic is requested.
Generated data features a compression level speed / ratio curve
which is more in line with expectation.
Yann Collet