Make settings display the addons tab if the addons directory exists in windows and mac too!
also improved the checking for the folder by using opendir, readdir and closedir.

Addon framework have also been changed so that you have 2 kinds of addons
1. OS specific addons
2. Universal(OS independent) addons

new structure is
$clientdir/modules/addons/$OS/
$clientdir/modules/addons/universal/

if your addon requires a non perl intercepter and is not a compiled binary
you can place the intercepter file inside (this will mostly only be useful on windows)
$clientdir/modules/addons/$OS/framework/$addonname/

NOTE: windows = MSWin32

universal modules (like platform independent perl modules) can be placed inside
$clientdir/modules/addons/universal/framework/perl/