Items added to main navigation get multiplied when header_site_navigation_tabs is extended with super()

[gocemitevski]

When using ckanext-pages with another CKAN extension that extends header.html, or the header_site_navigation_tabs block specifically, pages or blog posts added to the main navigation through the ckanext-pages UI, are shown once per super() call in the templates.

https://github.com/ckan/ckanext-pages/blob/master/ckanext/pages/plugin.py#L24

If header.html is extended three times in three separate extensions, each super() call will trigger the action for concatenating links in the navigation.

I already communicated this problem with @amercader and he recommended that I report it here.