Implement the "CGI bucket" in mod_cgi to handle stderr output during

Implement the "CGI bucket" in mod_cgi to handle stderr output during
script execution, preventing deadlock if stderr output fills the pipe
buffer:

* modules/generators/mod_cgi.c (log_script_err): Return a read error.
(cgi_bucket_create, cgi_bucket_dup, cgi_read_stdout, cgi_bucket_read):
New functions.
(cgi_handler): Use new CGI bucket rather than a pipe bucket if
APR_FILES_AS_SOCKETS; use zero read timeout from stdout/stderr during
script execution.

PR: 22030
Submitted by: Joe Orton, Jeff Trawick

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@103437 13f79535-47bb-0310-9956-ffa450edef68