[ruby] add a test for null shared_ptr in containers.

Examples/test-suite/ruby/cpp11_shared_ptr_nullptr_in_containers_runme.rb

@@ -0,0 +1,15 @@
+require "cpp11_shared_ptr_nullptr_in_containers"
+
+include Cpp11_shared_ptr_nullptr_in_containers
+
+a = ret_vec_c_shared_ptr()
+raise unless a[0].get_m == 0
+raise unless a[1]       == nil
+raise unless a[2].get_m == 2
+
+a = ret_arg_vec([C.new(7), nil, C.new(9)])
+raise unless a[0].get_m == 7
+raise unless a[1]       == nil
+raise unless a[2].get_m == 9
+
+raise unless is_last_null([C.new(7), C.new(8), nil])