Fix case of MAC special-values

This fixes Debian bug #596347. An alternative would be to also allow
the uppercase form, but it's not nice I think.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

man/gnt-backup.sgml

@@ -206,9 +206,8 @@
           <varlistentry>
             <term>mac</term>
             <listitem>
-              <simpara>either a value or <constant>GENERATE</constant>
-              to generate a new unique MAC, or
-              <constant>AUTO</constant> to reuse the old MAC</simpara>
+              <simpara>either a value or 'generate' to generate a new
+              unique MAC, or 'auto' to reuse the old MAC</simpara>
             </listitem>
           </varlistentry>
           <varlistentry>

man/gnt-instance.sgml

@@ -200,8 +200,8 @@
             <varlistentry>
               <term>mac</term>
               <listitem>
-                <simpara>either a value or <constant>GENERATE</constant>
-                  to generate a new unique MAC</simpara>
+                <simpara>either a value or 'generate' to generate a
+                  new unique MAC</simpara>
               </listitem>
             </varlistentry>
             <varlistentry>