Use cp1252 on Windows for the wxWidgets build too,

and add a note to the README about it.

buildtools/build_wxwidgets.py

@@ -160,7 +160,8 @@ def getoutput(cmd):
     output = None
     output = sp.stdout.read()
     if sys.version_info > (3,):
-        output = output.decode('utf-8')  # TODO: is utf-8 okay here?
+        outputEncoding = 'cp1252' if sys.platform == 'win32' else 'utf-8'        
+        output = output.decode(outputEncoding)
     output = output.rstrip()
     rval = sp.wait()
     if rval: