Python 2 Unicode strings can be used as inputs to char * or std::string types

Requires SWIG_PYTHON_2_UNICODE to be defined when compiling generated code.

Examples/test-suite/unicode_strings.i

@@ -2,6 +2,10 @@
 
 %include <std_string.i>
 
+%begin %{
+#define SWIG_PYTHON_2_UNICODE
+%}
+
 %inline %{
 
 const char* non_utf8_c_str(void) {
@@ -12,4 +16,8 @@ std::string non_utf8_std_string(void) {
         return std::string("h\xe9llo w\xc3\xb6rld");
 }
 
+char *charstring(char *s) {
+  return s;
+}
+
 %}