* Document the -P option

* Add a paragraph suggesting that the merge option be used only for
files that users have modified. People have been using this option
for all files that are different, causing unecessary confusion.

usr.sbin/mergemaster/mergemaster.8

@@ -32,7 +32,7 @@
 .Nd merge configuration files, et al during an upgrade
 .Sh SYNOPSIS
 .Nm
-.Op Fl scrvahipC
+.Op Fl scrvahipCP
 .Op Fl m Ar /path/to/sources
 .Op Fl t Ar /path/to/temp/root
 .Op Fl d
@@ -91,6 +91,12 @@ You can
 also specify that the script ignore the $Id strings and
 compare every file.
 .Pp
+The merge menu option is designed to let you easily combine your
+customizations from the old version of a file into the new one.
+While you can use the merge function to incorporate changes from
+files that you have not customized,
+it is not recommended.
+.Pp
 The
 .Nm
 utility checks your umask and issues a warning for anything
@@ -199,6 +205,12 @@ After a standard
 .Nm
 run,
 compares your rc.conf[.local] options to the defaults.
+.It Fl P
+Preserve files that you replace in
+.Pa /var/tmp/mergemaster/preserved-files-<date> ,
+or another directory you specify in your
+.Nm
+rc file.
 .It Fl m Ar /path/to/sources
 Specify the path to the directory where you want to do the
 .Xr make 1 .
@@ -316,6 +328,10 @@ with all values commented out:
 # Compare /etc/rc.conf[.local] to /etc/defaults/rc.conf
 #COMP_CONFS=yes
 #
+# Preserve files that you replace
+#PRESERVE_FILES=yes
+#PRESERVE_FILES_DIR=/var/tmp/mergemaster/preserved-files-`date +%y%m%d-%H%M%S`
+#
 # Sourcedir is the directory to do the 'make' in (where the new files are)
 #SOURCEDIR='/usr/src/etc'
 #