This commit looks for a new "extra-ref" attribute in <variablelist>
If this attribute is specified, its content will be index as pointing to
the current man-page in systemd.directives
name.tail = ''
name.text = text
formatting[text] = name
+ extra = variablelist.attrib.get('extra-ref')
+ if extra:
+ stor[extra].append((pagename, section))
+ if extra not in formatting:
+ elt = tree.Element("varname")
+ elt.text= extra
+ formatting[extra] = elt
storfile = directive_groups['filenames']
for xpath, absolute_only in (('.//refsynopsisdiv//filename', False),