Fix and simplify util.safewriter.SafeWriter

Storing the error encoding in an "encoding" attribute "breaks" the
python3 "input" function: In essence, builtin_input_impl does a
getattr(sys.stdout, 'encoding'), which returns our error encoding
instead of the "real" stdout encoding. In order to avoid this, we
store the error encoding in an "_encoding" attribute.

Making SafeWriter a new-style class simplifies the code a lot.

osc/util/safewriter.py

@@ -1,29 +1,23 @@
 # be careful when debugging this code:
 # don't add print statements when setting sys.stdout = SafeWriter(sys.stdout)...
-class SafeWriter:
+class SafeWriter(object):
     """
     Safely write an (unicode) str. In case of an "UnicodeEncodeError" the
     the str is encoded with the "encoding" encoding.
     All getattr, setattr calls are passed through to the "writer" instance.
     """
     def __init__(self, writer, encoding='unicode_escape'):
-        self.__dict__['writer'] = writer
-        self.__dict__['encoding'] = encoding
-
-    def __get_writer(self):
-        return self.__dict__['writer']
-
-    def __get_encoding(self):
-        return self.__dict__['encoding']
+        self._writer = writer
+        self._encoding = encoding
 
     def write(self, s):
         try:
-            self.__get_writer().write(s)
+            self._writer.write(s)
         except UnicodeEncodeError as e:
-            self.__get_writer().write(s.encode(self.__get_encoding()))
+            self._writer.write(s.encode(self._encoding))
 
     def __getattr__(self, name):
-        return getattr(self.__get_writer(), name)
+        return getattr(self._writer, name)
 
     def __setattr__(self, name, value):
-        setattr(self.__get_writer(), name, value)
+        super(SafeWriter, self).__setattr__(name, value)