(help_echo_object, help_echo_pos): New variables.

(help_echo_object, help_echo_pos): New variables.
(note_mode_line_highlight): Store additional information about the
help-echo in help_echo_object and help_echo_pos.  Check both
`local-map' and `keymap' properties for changing the cursor
(note_mouse_highlight): Store additional information about the
help-echo in help_echo_object and help_echo_pos.
(note_tool_bar_highlight): Set help_echo_object to nil and
help_echo_pos to -1.
(XTread_socket): Use gen_help_event instead of filling
input_events manually.
(syms_of_xterm): Staticpro help_echo_object.