Fix dead-binding detection in Rebinder.
Fix dead-binding detection in Rebinder.

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