Set created_at correctly when sessions are created.
Merge branch 'master' of git://github.com/cdd/smart_session_store

* 'master' of git://github.com/cdd/smart_session_store:
  Set created_at correctly when sessions are created.

Conflicts:
	lib/mysql2_session.rb
	lib/mysql_session.rb
	lib/postgresql_session.rb
	lib/sqlite_session.rb