r->headers_in is shared by original requests and components (make no sense

copy them for components), but each component has its own r->pool.
So once the first component set "Max-Forwards", it is in headers_in
but the value could get lost with the first component's r->pool.
Hence I sometimes see "Max-Forwards" has value like letter "l".
Change it to use apr_table_set() fixed the problem.

Submitted by:	Jin Hong <jinh@cnet.com>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92253 13f79535-47bb-0310-9956-ffa450edef68