Allow swapping wxString iterators in C++11 mode

Specialize std::iter_swap() for wxString::iterator in C++11 mode as the
default implementation of it doesn't work for iterators using "reference" type
different from "value_type&" as is the case for wxString::iterator.

This notably allows the code using std::reverse() with wxString iterators to
compile in C++11 mode, which wasn't the case before.

include/wx/string.h

@@ -3986,6 +3986,29 @@ namespace std
 
 #endif // C++11
 
+// Specialize std::iter_swap in C++11 to make std::reverse() work with wxString
+// iterators: unlike in C++98, where iter_swap() is required to deal with the
+// iterator::reference being different from "iterator::value_type&", in C++11
+// iter_swap() just calls swap() by default and this doesn't work for us as
+// wxUniCharRef is not the same as "wxUniChar&".
+#if __cplusplus >= 201103L
+
+namespace std
+{
+    template <>
+    inline void
+    iter_swap<wxString::iterator>(wxString::iterator i1, wxString::iterator i2)
+    {
+        // We don't check for i1 == i2, this won't happen in normal use, so
+        // don't pessimize the common code to account for it.
+        wxUniChar tmp = *i1;
+        *i1 = *i2;
+        *i2 = tmp;
+    }
+} // namespace std
+
+#endif // C++11
+
 // ---------------------------------------------------------------------------
 // Implementation only from here until the end of file
 // ---------------------------------------------------------------------------