New patch after review by Éric Araujo. The difference between the last one and the current is cosmetic:

--- Lib/configparser.py 2010-07-27 11:36:51.000000000 +0200
+++ Lib/configparser.py.2       2010-07-28 13:05:39.000000000 +0200
@@ -117,3 +117,2 @@
 import re
-import sre_parse
 import sys
@@ -140,2 +139,3 @@
         BaseException."""
+
         return self.__message
@@ -145,2 +145,3 @@
         BaseException."""
+
         self.__message = value
@@ -301,2 +302,3 @@
         """
+
         if section.lower() == "default":
@@ -338,2 +340,3 @@
         """
+
         if isinstance(filenames, str):
@@ -358,4 +361,4 @@
         used.
-
         """
+
         if filename is None:
@@ -419,2 +422,3 @@
         """Check for the existence of a given option in a given section."""
+
         if not section or section == DEFAULTSECT:
@@ -431,2 +435,3 @@
         """Set an option."""
+
         if not section or section == DEFAULTSECT:
@@ -444,2 +449,3 @@
            between keys and values are surrounded by spaces."""
+
         if space_around_delimiters:
@@ -456,2 +462,3 @@
         """Remove an option."""
+
         if not section or section == DEFAULTSECT:
@@ -471,2 +478,3 @@
         """Remove a file section."""
+
         existed = section in self._sections
@@ -529,2 +537,3 @@
         """
+
         cursect = None                     # None, or a dictionary
@@ -657,2 +666,3 @@
         """
+
         d = self._defaults.copy()
@@ -690,2 +700,3 @@
         """
+
         d = self._defaults.copy()
@@ -789,2 +800,3 @@
         """Set an option.  Extend ConfigParser.set: check for string values."""
+
         # The only legal non-string value if we allow valueless



Some remarks on Éric's review:
- thanks for reviewing the patch, however you did review an outdated version
- comment_prefixes are by all means prefixes. Collins dictionary: "prefix, n. - 2. something coming or placed before". Other reviewers didn't pose the current name as inapt
- other remarks corrected in the current patch