Change ap_send_fd() so that it returns a proper apr_status_t value

Change ap_send_fd() so that it returns a proper apr_status_t value
instead of the number of bytes sent.

default_handler() ignores the ap_send_fd() return code, but
mod_file_cache doesn't.  When mod_file_cache's handler called
ap_send_fd(), the client would get the desired file plus an
error document (500 internal server error), which was delivered
because mod_file_cache's handler returned an error since
ap_send_fd() returned non-zero.

Also in this commit is a hack to be able to compile when APACHE_XLATE
is defined.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86380 13f79535-47bb-0310-9956-ffa450edef68