If the tags page was visited with "tags.php" via, say,
the sidebar heading, the urls made with the template
were broken; the query string was joined to the baseurl
with a & rather than a ?. This patch checks if the last
8 characters are tags.php and sets a queryprefix value
based on the result.

Change-Id: I56f87b76e9fb82472fda2c6cb2c5315bb3f79c05
Signed-off-by: Melissa Draper <melissa@catalyst.net.nz>