Only call bflush() after sending the header if we are using

keep-alives, to workround a netscape bug; otherwise it hurts
performance.

Submitted by: drtr@ast.cam.ac.uk (David Robinson)
Obtained from: 116.keepalive_flush.patch


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@76337 13f79535-47bb-0310-9956-ffa450edef68