Fix prettyprinting of things like x/y*z.
Fix prettyprinting of things like x/y*z.

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