man/groupadd.8.xml: clarify the exit values meaning.
man/groupmod.8.xml: clarify the E_GID_IN_USE value meaning.
<varlistentry>
<term><replaceable>4</replaceable></term>
<listitem>
- <para>GID not unique (when <option>-o</option> not used)</para>
+ <para>GID is already used (when called without <option>-o</option>)</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable>9</replaceable></term>
<listitem>
- <para>group name not unique</para>
+ <para>group name is already used</para>
</listitem>
</varlistentry>
<varlistentry>
<varlistentry>
<term><replaceable>4</replaceable></term>
<listitem>
- <para>E_GID_IN_USE: specified group doesn't exist</para>
+ <para>E_GID_IN_USE: group id already in use</para>
</listitem>
</varlistentry>
<varlistentry>