replace tep_session_id() and tep_session_name() calls to native equivalents
replace tep_session_save_path() calls to native equivalent
remove tep_session_close() function, remove call in application_bottom as session_write_close() is being registered as a shutdown function when the session starts
Merge pull request #155 from haraldpdl/superglobals

superglobals - sessions
replace tep_session_is_registered() with isset()
Merge pull request #156 from haraldpdl/superglobals

replace tep_session_is_registered() with isset()
replace tep_session_unregister() with unset()
Merge pull request #157 from haraldpdl/superglobals

replace tep_session_unregister() with unset()