Use ap_select instead of select in ab, and replace hardcoded 256 with

FD_SETSIZE.  Should really dynamically track the highest descriptor
and use that.

PR: 2625
Obtained from:
Submitted by:	Richard Lloyd <rkl@connect.org.uk>, Marc Slemko
Reviewed by:


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/1.3.x@81749 13f79535-47bb-0310-9956-ffa450edef68