Fix ToSigned/ToUnsigned prettyprinting.
Fix ToSigned/ToUnsigned prettyprinting.

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