use merge param in compare link for it to work as expected

rhodecode/templates/base/base.html

@@ -123,7 +123,7 b''
                %endif
              %endif
               %if c.rhodecode_db_repo.fork:
-               <li>${h.link_to(_('Compare fork'),h.url('compare_url',repo_name=c.rhodecode_db_repo.fork.repo_name,org_ref_type='branch',org_ref='default',other_repo=c.repo_name,other_ref_type='branch',other_ref=request.GET.get('branch') or 'default'),class_='compare_request')}</li>
+               <li>${h.link_to(_('Compare fork'),h.url('compare_url',repo_name=c.rhodecode_db_repo.fork.repo_name,org_ref_type='branch',org_ref='default',other_repo=c.repo_name,other_ref_type='branch',other_ref=request.GET.get('branch') or 'default', merge=1),class_='compare_request')}</li>
               %endif
               <li>${h.link_to(_('Lightweight changelog'),h.url('shortlog_home',repo_name=c.repo_name),class_='shortlog')}</li>
               <li>${h.link_to(_('Search'),h.url('search_repo',repo_name=c.repo_name),class_='search')}</li>