Moved the cart item class into its own php file, updated the file comments
Include cart item class php file that was split out of the cart class php file
Deprecated cart item meta functions that sent data to central meta data table
Save cart item meta implemented using new wp-e-commerce meta data infrastructure
Check only the session_id() result to determine if a session is active, as suggested by benhuson in #552
Merge branch 'fix-session-start-working'