ap_bvputs() is a misnomer; introduce ap_bputstrs()

    [todo: proxy and file_cache code should be updated for new name]
add ap_vbputstrs()
use ap_vbputstrs() from http_protocol.
use EOF in a few places, rather than the magic "-1" constant


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85589 13f79535-47bb-0310-9956-ffa450edef68