(Fx_get_resource): Major rewrite to make it clearer.

(Fx_get_resource): Major rewrite to make it clearer.
(validate_x_resource_name): Use build_string, not make_string.
(Fx_create_frame): Initially use Vinvocation_name as resource name.
Switch to frame name if frame name is explicit.
(x_display_info_for_name, Fx_open_connection): Add casts.
Initially use Vinvocation_name as resource name.
[USE_X_TOOLKIT] (x_window): Use Vx_resource_name for widget names.