Fix integer overflow in ap_pregsub. This can be triggered e.g.

with mod_setenvif via a malicious .htaccess

CVE-2011-3607
http://www.halfdog.net/Security/2011/ApacheModSetEnvIfIntegerOverflow/


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1198940 13f79535-47bb-0310-9956-ffa450edef68