Populates Category:Redirects from merges

Note to editors considering use of this template: when merging a page into another, please replace the entire markup in its edit pane (in a page, not section, edit), so the entire markup saved is

#REDIRECT [[Title of article that former article was merged into]] {{R from merge}}

followed by the category links, and/or additional maintenance templates, if any, required by the redirect. If the content has been merged to a specific section or list entry, {{R to section}} or {{R to list entry}} may be appropriate.