Update autogen.sh

The m4 directory must not be removed as it contains files
which are distributed with the source code.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

autogen.sh

@@ -40,8 +40,7 @@
 if [ "$1" = "clean" ]; then
     echo "Cleaning..."
     rm configure aclocal.m4
-    rm m4/*
-    rmdir m4
+    rm m4/l*
     rm config/*
     rmdir config
     find . -iname "Makefile.in" -type f -exec rm '{}' +
@@ -60,11 +59,6 @@ else
   bail_out
 fi
 
-# create m4 directory if it does not exist
-if [ ! -d m4 ];  then
-    mkdir m4
-fi
-
 bail_out()
 {
     echo