Fixed the handling of module and script-added header fields.

Improved the interface for sending header fields and reduced
the duplication of code between sending okay responses and errors.
We now always send both headers_out and err_headers_out, and
ensure that the server-reserved fields are not being overridden,
while not overriding those that are not reserved.

Fixed the determination of whether or not we should make the
connection persistent for all of the cases where some other part
of the server has already indicated that we should not.  Also
improved the ordering of the test so that chunked encoding will
be set whenever it is desired instead of only when KeepAlive
is enabled. Added persistent connection capability for most error
responses (those that do not indicate a bad input stream) when
accessed by an HTTP/1.1 client.

Added missing timeouts for sending header fields, error responses,
and the last chunk of chunked encoding, each of which could have
resulted in a process being stuck in write forever.

Reviewed by: Randy Terbush, Dean Gaudet


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@77741 13f79535-47bb-0310-9956-ffa450edef68