Fixes for pbi paths and update to 1.5.1 php front end

vnstat.inc changes:
Updated vnstat_php_front end to 1.5.1-updated
Added checks for i386 & amd64 pbi paths 
If file_exists create links for i386 & amd64 paths
Move pfsense style to external themes for 1.5.1

You can get the php front end 1.5.1-updated from my fork but be sure to rename the file!!! There are dashes in the download instead of underscores.

https://github.com/parawizard/vnstat-php-frontend

or go here

http://www.sendspace.com/file/0py5vt