Reimplement ap_send_fd. Eliminate ap_send_fd_length. If APR_HAS_SENDFILE is

defined but ap_sendfile fails with APR_ENOTIMPL, the BUFF implementation
of ap_send_fd will get a shot at serving the request.  This fix is
required to get Apache working on 95/98 again and can also be useful on
Unix systems where sendfile is available via a servicepack/fixpack/PTF
on a particular level of the OS (e.g., AIX 4.3.2 base does not include
sendfile but is is available with a PTF).

This fix also reimplements the mod_file_cache sendfile_handler using
ap_send_fd and sets the connection aborted flag if the sendfile fails.

Future modification... Add code to ap_send_fd to hijack any data in the
client BUFF structure and send it along with the sendfile.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85810 13f79535-47bb-0310-9956-ffa450edef68