Ensure ampersands in URLs are & per HTML spec

Ensure ampersands in URLs are & per HTML spec

The propagator variable defined in parts/header.tt2 holds the value
of the CGI query string - which, as it comes off the wire, is a simple
"&". The problem with this is perhaps best explained at
http://www.htmlhelp.com/tools/validator/problems.html#amp (and it
explains why "&copy_..." gets converted into a copyright symbol).

By passing the incoming query string through the TT url filter and
then replacing "&" with "&" we avoid this problem at the source.
From there, we have to address the other locations in the code in
which we are manually appending GET variables.

Signed-off-by: Dan Scott <dan@coffeecode.net>