Clear errno before calling strtol, and add in some comments.

Obtained from:  Philippe M. Chiasson <gozer@cpan.org>,
                Geoffrey Young <geoff@modperlcookbook.org>
Submitted by:	Aaron Bannert


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@97578 13f79535-47bb-0310-9956-ffa450edef68