[BUG] Important bug fix in an optimization.

Reduction(axis!=0) of joins(axis=0) wasn't working on the right axis.

NEWS.txt
- BUG: optimization bug fix that caused Reduction(axis!=0) of joins(axis=0) wasn't working on the right axis. (Frederic B., reported by Marc-Alexandre Cote)

no news.txt, it also fix a crash in debugmode introduced after the last release. It was a debugmode speed up that introduced that.