Add session_class, which defines a JSObject wrapper for struct session.
Add location_array_class, which defines a JSObject wrapper for struct
ses_history. The "history" member of struct session is a struct
ses_history, which is a linked list of struct location.
Add a pointer from struct session to the session_class object and the
location_array object.
Add smjs_get_session_object to return a session_class JSObject wrapper for
a given struct session.
Add smjs_get_session_location_array_object to return a location_array_class
JSObject wrapper for a given struct session.
Add "session" property to the "elinks" object, which uses
smjs_get_session_object to get a JSObject wrapper for smjs_ses.
Add smjs_location_array_get_property, which allows indexing
a location_array object using a positive number for history forward or
a negative number for history backward.
Add session_props, session_get_property, session_set_property,
session_funcs, smjs_session_goto_url (which implements the "goto" method),
and smjs_init_session_interface for session_class.
Add session_construct, which creates a new tab and returns the JSObject
session_class wrapper.
Add session_finalize and smjs_location_array_finalize, which clear the
pointers between struct session and the JSObject wrappers in question.
Add smjs_detach_session_object, which clears the pointers between a given
struct session and the corresponding JSObject wrappers.
In destroy_session, call smjs_detach_session_object.
Add jsval_to_object helper in ecmascript/spidermonkey/util.h;
jsval_to_object is used in smjs_session_goto_url.
Modify delayed_goto_uri_frame to allow the target to be NULL.
smjs_session_goto_url needs this modification.
