If we are using -p it does not make any sense to even create the

MTREENEW file since it will never be used.

usr.sbin/mergemaster/mergemaster.sh

@@ -686,9 +686,9 @@ case "${RERUN}" in
   find -d ${TEMPROOT} -type d -empty -delete 2>/dev/null
 
   # Build the mtree database in a temporary location.
-  MTREENEW=`mktemp -t mergemaster.mtree`
   case "${PRE_WORLD}" in
-  '') mtree -ci -p ${TEMPROOT} -k size,md5digest > ${MTREENEW} 2>/dev/null
+  '') MTREENEW=`mktemp -t mergemaster.mtree`
+      mtree -ci -p ${TEMPROOT} -k size,md5digest > ${MTREENEW} 2>/dev/null
       ;;
   *) # We don't want to mess with the mtree database on a pre-world run or
      # when re-scanning a previously-built tree.