Removed what appears to be dead/unreachable code within constants.php and added a new IS_WINDOWS constant.

Reasoning behind the removal:
* DIRECTORY_SEPARATOR is always defined (at least according to the PHP manual)
* PATH_SEPARATOR exists since php 4.3.0, and Revive requires PHP 5.1.4+ at the very least so...

Source: http://www.php.net/manual/en/dir.constants.php
Fix #309 - Allow separate cookie domain for OAID
Fix #337 - video tracking through https
Regenerated plugins

Commits:
 * Fix #337 - video tracking through https
Ref #337 - Release note
Merge branch '309-cookies'
Updated notes for #309
Regenerated delivery scripts

Commits:
 * Fix #309 - Allow separate cookie domain for OAID
 * Merge branch '309-cookies'
 * Updated notes for #309
Skip memcache test, if not available
Really skip testin case memcache is not available
Fixed fc.php being used twice in 695ac7 - ref #337
Regenerated plugins

Commits:
 * Fixed fc.php being used twice in 695ac7 - ref #337
Merge pull request #334 from zytzagoo/fixing-constants

Removed dead/unreachable code in constants.php

Also added a new IS_WINDOWS constant that might come in handy.