selftest: explain how the message command test works

selftest/target/Samba3.pm

@@ -872,6 +872,8 @@ sub provision($$$$$$$)
 
         resolv:host file = $dns_host_file
 
+        # The samba3.blackbox.smbclient_s3 test uses this to test that
+        # sending messages works, and that the %m sub works.
         message command = mv %s $shrdir/message.%m
 
 	# Begin extra options

source3/script/tests/test_smbclient_s3.sh

@@ -260,6 +260,7 @@ EOF
 	return
     fi
 
+    # The server writes this into a file message.msgtest, via message.%m to test the % sub code
     cmd='$SMBCLIENT "$@" -U$USERNAME%$PASSWORD //$SERVER/tmpguest -p 139 $ADDARGS -c "get message.msgtest $PREFIX/message_out.$$" 2>&1'
     eval echo "$cmd"
     out=`eval $cmd`