[Fix][#33829] Use 404 response codes when server URL rewriting is enabled

Joomla Code Tracker: http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=33829&start=0

 How to test:

Install Joomla 3.3.0 with some sample data on an apache server.

In the Site Settings, enable:
1. Search Engine Friendly URLs
2. Use URL rewriting
3. Adds Suffix to URL

Rename htaccess.txt to .htaccess to enable URL rewriting on the server.
 
Enter a URL for a non-existent file (assume the Joomla installation is at http://example.com):
http://examle.com/images/missing-file.pdf

The expected response is a "404" (not found) error.

The actual response is a "500" (internal server error) response.  This response is misleading.  There has been no "server error" -- it's simply a case of the client requesting a file that was not found on the server.

The issue is further exacerbated with the recent merging of pull request #488, because now any missing file with any file extension will be redirected to Joomla.  If the file ends with anything other than ".html", the response will likely be 500 rather than 404.

This problem also affects the Redirect component.  Although redirects can be created for missing files, the redirects will not be honored.  An example redirect:

http://examle.com/images/missing-file.pdf -> http://example.com/index.php

Such a redirect will fail because it would only be honored when a 404 error
condition is encountered.

This issue is probably the same as issue #30344, but that was closed due to inactivity.