Merge r535617 from trunk: (fixes CVE-2007-1863)

* Prevent a segmentation fault if one of the Cache-Control headers
  s-maxage, max-age, min-fresh, max-stale has no value assigned.
  In this case ignore s-maxage, max-age, min-fresh. For max-stale
  it is valid to set no value. In this case set max-stale to 1 year
  to signal that the client is accepting a stale response of any age.

Submitted by: Niklas Edmundsson <nikke acc.umu.se>
Reviewed by: mjc, rpluem, jorton


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@551944 13f79535-47bb-0310-9956-ffa450edef68