Added FacebookPageTabHelper
Updated PageTabHelper
Merge pull request #97 from facebook/gFosco.pagetab

Added FacebookPageTabHelper
Updated session validation for app sessions and pages
Merge pull request #98 from facebook/gFosco.expires

Updated session validation for app sessions and pages
added throws phpdoc tag
Merge pull request #99 from irfanevrens/patch-1

added throws phpdoc tag