Description:
------------
I have discovered that the built-in php web server sends a default Content-Type 
header (text/html) when responding with HTTP/1.1 304 Not Modified.  This clobbers 
the Content-Type stored in a cache and violates RFC2616-10.3.5 
(http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5)

"If the conditional GET used a strong cache validator (see section 13.3.3), the 
response SHOULD NOT include other entity-headers. Otherwise (i.e., the 
conditional GET used a weak validator), the response MUST NOT include other 
entity-headers; this prevents inconsistencies between cached entity-bodies and 
updated headers."

I have found related tickets related the Apache.  This ticket differs only in 
that it refers to the built-in web server.

Test script:
---------------
<?php

header('HTTP/1.1 304 Not Modified');

Expected result:
----------------
HTTP/1.1 304 Not Modified
Host: localhost:8001
Connection: close
X-Powered-By: PHP/5.4.14

Actual result:
--------------
HTTP/1.1 304 Not Modified
Host: localhost:8001
Connection: close
X-Powered-By: PHP/5.4.14
Content-type: text/html