Including "replace" argument in the header() function callback.
This change required code changes in PHP.c:mod_header_handler
and doc changes in PHP.pm.

In test script, call Test::More::BAIL_OUT if the 'use PHP'
call fails with a "Can't locate loadable object for module ..."
message. That usually means that the php lib does not have
embedded SAPI compiled into it, and that the tester can not
use this module.
Log last checkin in Changes file
Test cases for 2nd argument to header callback