string.h needs to be included before monkeying around with strchr et al,

since some system header files do their own monkeying around with those
functions in ways that don't get along with us unless we include their
definitions first

examples: gcc 2.8.1 on Solaris
          gcc 2.95.2 on AIX


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@88113 13f79535-47bb-0310-9956-ffa450edef68