avoid issues when env has been aliased

Closes #325

z.sh

@@ -95,10 +95,10 @@ _z() {
         ' 2>/dev/null >| "$tempfile"
         # do our best to avoid clobbering the datafile in a race condition.
         if [ $? -ne 0 -a -f "$datafile" ]; then
-            env rm -f "$tempfile"
+            \env rm -f "$tempfile"
         else
             [ "$_Z_OWNER" ] && chown $_Z_OWNER:"$(id -ng $_Z_OWNER)" "$tempfile"
-            env mv -f "$tempfile" "$datafile" || env rm -f "$tempfile"
+            \env mv -f "$tempfile" "$datafile" || \env rm -f "$tempfile"
         fi
 
     # tab completion