* Reduce diffs to RELENG_4 by specifying a full path to sysctl

* Adjust a little whitespace
* Make the distrib-dirs/mtree on DESTDIR conditional on user
  actually specifying a DESTDIR. This seemed like a safe
  way to get the right directories and permissions in the
  installed tree since 'make installworld' does the same
  thing, but in practice too many people have custom hacks
  that we should leave unmolested. Still need to find a way
  to deal with 'install -d' and permissions on nonexistent
  directories in the middle of the path, but this is at
  least no worse that it was before.

PR:		bin/22661

usr.sbin/mergemaster/mergemaster.8

@@ -295,7 +295,7 @@ with all values commented out:
 #DONT_CHECK_PAGER=
 #
 # If you set 'yes' above, make sure to include the PATH to your pager
-#PATH=/bin:/usr/bin:/usr/sbin:/sbin
+#PATH=/bin:/usr/bin:/usr/sbin
 #
 # Don't compare the old and new motd files
 #IGNORE_MOTD=yes

usr.sbin/mergemaster/mergemaster.sh

@@ -10,7 +10,7 @@
 
 # $FreeBSD$
 
-PATH=/bin:/usr/bin:/usr/sbin:/sbin
+PATH=/bin:/usr/bin:/usr/sbin
 
 display_usage () {
   VERSION_NUMBER=`grep "[$]FreeBSD:" $0 | cut -d ' ' -f 4`
@@ -124,6 +124,7 @@ diff_loop () {
         echo ''
         if mm_install "${COMPFILE}"; then
           echo "   *** ${COMPFILE} installed successfully"
+          echo ''
           # Make the list print one file per line
           AUTO_INSTALLED_FILES="${AUTO_INSTALLED_FILES}      ${DESTDIR}${COMPFILE#.}
 "
@@ -428,7 +429,12 @@ case "${RERUN}" in
   esac
 
   { cd ${SOURCEDIR} &&
-    make DESTDIR=${DESTDIR} distrib-dirs &&
+    case "${DESTDIR}" in
+    '') ;;
+    *)
+      make DESTDIR=${DESTDIR} distrib-dirs
+      ;;
+    esac
     make DESTDIR=${TEMPROOT} distrib-dirs &&
     make DESTDIR=${TEMPROOT} -DNO_MAKEDEV distribution;} ||
   { echo '';
@@ -475,7 +481,7 @@ case "${RERUN}" in
   esac
 
   # Avoid trying to update MAKEDEV if /dev is on a devfs
-  if sysctl vfs.devfs.generation > /dev/null 2>&1 ; then
+  if /sbin/sysctl vfs.devfs.generation > /dev/null 2>&1 ; then
     rm ${TEMPROOT}/dev/MAKEDEV ${TEMPROOT}/dev/MAKEDEV.local
   fi