Cleanup the suEXEC support in APACI and make it more safe:

 1. Add big fat hint in INSTALL about risks and to read the
    htdocs/manual/suexec.html document before using the suexec-related
    configure options.

 2. Make sure the user has at least provided one --suexec-xxxx option
    (specifies suEXEC parameters) in addition to --enable-suexec option.
    If only --enable-suexec is given APACI stops with a hint to INSTALL
    and htdocs/manual/suexec.html documents.

 3. Provide two additional --suexec-xxxx options to make the suEXEC
    configuration complete (especially for package maintainers who else
    had to patch the source tree) by providing ways to configure minimal
    UID/GID and safe PATH, too.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81187 13f79535-47bb-0310-9956-ffa450edef68