Python 3.7 support: Remove use of deprecated PyUnicode_GetSize

CHANGES.current

@@ -16,8 +16,12 @@ Version 4.0.0 (in progress)
 
               instring(b"h\xe9llooo") # Python
 
+2018-06-15: wsfulton
+            [Python] Python 3.7 support: Replace use of deprecated PyUnicode_GetSize with
+            PyUnicode_GetLength to remove deprecated warnings compiling the C/C++ wrappers.
+
 2018-06-12: wsfulton
-            [Python] The %pythonabc feature in pyabc.i now uses base classes
+            [Python] Python 3.7 support: The %pythonabc feature in pyabc.i now uses base classes
               collections.abc.MutableSequence
               collections.abc.MutableMapping
               collections.abc.MutableSet

Lib/python/pywstrings.swg

@@ -29,7 +29,11 @@ SWIG_AsWCharPtrAndSize(PyObject *obj, wchar_t **cptr, size_t *psize, int *alloc)
   }
 %#endif
   if (isunicode) {
+%#if PY_VERSION_HEX >= 0x03030000
+    Py_ssize_t len = PyUnicode_GetLength(obj);
+%#else
     Py_ssize_t len = PyUnicode_GetSize(obj);
+%#endif
     if (cptr) {
       Py_ssize_t length;
       *cptr = %new_array(len + 1, wchar_t);