[ruby] add std::wstring tests for string including a null terminator.

Examples/test-suite/ruby/li_std_wstring_runme.rb

@@ -35,3 +35,8 @@ begin
 rescue RuntimeError => e
   swig_assert_equal("e.message", "'x'", binding)
 end
+
+x = "abc\0def"
+swig_assert_equal("Li_std_wstring.test_value(x)", "x", binding)
+swig_assert_equal("Li_std_wstring.test_ccvalue(x)", '"abc"', binding)
+swig_assert_equal("Li_std_wstring.test_wchar_overload(x)", '"abc"', binding)

Lib/ruby/std_wstring.i

@@ -26,7 +26,7 @@ extern "C" {
 
 /**
  *  If Encoding.default_internal is nil, this encoding will be used
- *  when coverting from std::wstring to String object in Ruby.
+ *  when converting from std::wstring to String object in Ruby.
  */
 #ifndef SWIG_RUBY_INTERNAL_ENCODING
 #define SWIG_RUBY_INTERNAL_ENCODING "UTF-8"