fixed bug in reduce optimizer (also keep variable mapping for variables which map onto their old position)
fixed bug in reduce optimizer (also keep variable mapping for variables which
map onto their old position)

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb