A few fixes to scanT uniqueness typing.
A few fixes to scanT uniqueness typing.

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