mod_cgi, mod_cgid, mod_ext_filter: Log errors when scripts cannot

mod_cgi, mod_cgid, mod_ext_filter: Log errors when scripts cannot
be started on Unix because of such problems as bad permissions,
bad shebang line, etc.

Some minor points:

If mod_ext_filter debug is enabled, we go ahead and burn cycles
in the parent to try to discover when we won't be able to exec
the script.

The mod_cgid handler wasn't communicating the right log level to the
daemon; that was required to get the child errfn to spit out the
right message, and it may fix an existing problem.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@98630 13f79535-47bb-0310-9956-ffa450edef68