Use "const char * const *" for process->argv (which is the correct

Use "const char * const *" for process->argv (which is the correct
const-ness since we sometimes put "some string" in there, and also the CRT's
argv). propagate this change within http_main and mpm/winnt/ (also correct
some other const type usage within the MPM).

fix ab's call to parse_url() which removed a const to actually manipulate an
arg from the CRT's argv (indirectly via opt->arg). no idea how this has
avoided segfaulting.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87130 13f79535-47bb-0310-9956-ffa450edef68