Disable exploitation of commutative reductions.
Disable exploitation of commutative reductions.

It broke in kmeans.  Will fix eventually, maybe.

diku-dk/futhark,diku-dk/futhark,mrakgr/futhark,ihc/futhark,diku-dk/futhark,ihc/futhark,mrakgr/futhark,HIPERFIT/futhark,diku-dk/futhark,HIPERFIT/futhark,HIPERFIT/futhark,ihc/futhark,diku-dk/futhark,CulpaBS/wbBach,mrakgr/futhark