Make it more clear in the docs that -a is not compatible with -iFU,

and enforce this in the code. Apparently a lot of users mistakenly
combine -a with these flags and are then mystified that no changes
were made.

While I'm here, fix a trailing space in mergemaster.8

usr.sbin/mergemaster/mergemaster.8

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 7, 2010
+.Dd March 13, 2010
 .Dt MERGEMASTER 8
 .Os
 .Sh NAME
@@ -32,7 +32,8 @@
 .Nd merge configuration files, et al during an upgrade
 .Sh SYNOPSIS
 .Nm
-.Op Fl scrvahipFCPU
+.Op Fl scrvhpCP
+.Op Fl a|iFU
 .Op Fl m Ar /path/to/sources
 .Op Fl t Ar /path/to/temp/root
 .Op Fl d
@@ -206,9 +207,11 @@ If the
 directory exists, it creates a new one in a previously
 non-existent directory.
 This option unsets the verbose flag,
-but other than
-.Fl U
-it is compatible with all other options.
+and is not compatible with
+.Fl i ,
+.Fl F ,
+or
+.Fl U .
 Setting
 .Fl a
 makes

usr.sbin/mergemaster/mergemaster.sh

@@ -15,7 +15,7 @@ PATH=/bin:/usr/bin:/usr/sbin
 display_usage () {
   VERSION_NUMBER=`grep "[$]FreeBSD:" $0 | cut -d ' ' -f 4`
   echo "mergemaster version ${VERSION_NUMBER}"
-  echo 'Usage: mergemaster [-scrvahipFCPU]'
+  echo 'Usage: mergemaster [-scrvhpCP] [-a|[-iFU]]'
   echo '    [-m /path] [-t /path] [-d] [-u N] [-w N] [-A arch] [-D /path]'
   echo "Options:"
   echo "  -s  Strict comparison (diff every pair of files)"
@@ -337,6 +337,18 @@ while getopts ":ascrvhipCPm:t:du:w:D:A:FU" COMMAND_LINE_ARGUMENT ; do
   esac
 done
 
+if [ -n "$AUTO_RUN" ]; then
+  if [ -n "$FREEBSD_ID" -o -n "$AUTO_UPGRADE" -o -n "$AUTO_INSTALL" ]; then
+    echo ''
+    echo "*** You have included the -a option along with one or more options"
+    echo '    that indicate that you wish mergemaster to actually make updates'
+    echo '    (-F, -U, or -i), however these options are not compatible.'
+    echo '    Please read mergemaster(8) for more information.'
+    echo ''
+    exit 1
+  fi
+fi
+
 # Assign the location of the mtree database
 #
 MTREEDB=${MTREEDB:-${DESTDIR}/var/db}