Goal: accepts the -O flag for backward compatibility. (was used by adduser?)

Note: useradd.8 needs to be regenerated.

Status wrt upstream: not included as this is just specific 
                     backward compatibility for Debian

--- a/man/useradd.8.xml
+++ b/man/useradd.8.xml
@@ -300,6 +300,11 @@
 	    <replaceable>UID_MIN</replaceable>=<replaceable>10</replaceable>,<replaceable>UID_MAX</replaceable>=<replaceable>499</replaceable>
 	    doesn't work yet.
 	  </para>
+          <para>
+            For the compatibility with previous Debian's
+            <command>useradd</command>, the <option>-O</option> option is
+            also supported.
+          </para>
 	</listitem>
       </varlistentry>
       <varlistentry>
