Patch by Arfrever
http://sourceforge.net/tracker/?func=detail&aid=3598893&group_id=38414&atid=422030

Index: docutils/frontend.py
===================================================================
--- docutils/frontend.py	(revision 7578)
+++ docutils/frontend.py	(working copy)
@@ -158,7 +158,7 @@
 
 def validate_colon_separated_string_list(
     setting, value, option_parser, config_parser=None, config_section=None):
-    if isinstance(value, unicode):
+    if isinstance(value, basestring):
         value = value.split(':')
     else:
         last = value.pop()
@@ -171,7 +171,7 @@
     """
     # `value` is already a list when  given as command line option
     # and "action" is "append"
-    if isinstance(value, unicode):
+    if isinstance(value, basestring):
         value = [value]
     # this function is called for every option added to `value`
     # -> split the last item and apped the result:
@@ -731,7 +731,7 @@
         """Wrapper around sys.stderr catching en-/decoding errors"""
 
     def read(self, filenames, option_parser):
-        if type(filenames) in (str, unicode):
+        if isinstance(filenames, basestring):
             filenames = [filenames]
         for filename in filenames:
             try: