Improve the heuristic for deciding when to use writev() vs. when to

copy into the buffer.  No sense copying if the copy would fill
the buffer, might as well writev and start a fresh buffer.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@78832 13f79535-47bb-0310-9956-ffa450edef68