Fix hang after C-z in gnome-shell.

Fix hang after C-z in gnome-shell.

* xterm.c: Declare x_handle_net_wm_state to return int.
(handle_one_xevent): Check if we are iconified but don't have
_NET_WM_STATE_HIDDEN.  If do, treat as deiconify.
(get_current_wm_state): Return non-zero if not hidden,
check for _NET_WM_STATE_HIDDEN (Bug#9893).
(do_ewmh_fullscreen): Ignore return value from get_current_wm_state.
(x_handle_net_wm_state): Return what get_current_wm_state returns.
(x_term_init): Initialize dpyinfo->Xatom_net_wm_state_hidden.

* xterm.h (x_display_info): Add Xatom_net_wm_state_hidden (Bug#9893).