Patch to add support for entering PHP code and some caching support

Hi

I needed this slightly changed so I could set the taxonomy term path according to the current "section" of the site. E.g. I wanted it to be different for /about/ and for /contact/.

Sorry, patch got quite lengthy.

Just to give an example for a code snippet for the term path:

$s = explode('/',request_uri());
if($s[1]) {
  echo $s[1].'/tags/!name';
  return;
}
echo 'all/tags/!name';

There's also a bit of caching code now to reduce the number of database queries. It does that by storing the path for each vocabulary after the first call inside the request.