Function names for sidebar tag list collide

The patch to add tag support for Wiki pages implements the same function names for issues and wiki pages for the sidebar tag list. In my system (redmine 2.1.6, ruby 1.9.3p0), this caused the functions from wiki_sidebar_patch to be called when trying to render the issues page. This meant that no tags were displayed. This patch renames the functions so they no longer collide and the issues tag list is displayed when accessing the issues page.