Use utf-8 to encode files by default.

Should fix this bug in Seen:
Traceback (most recent call last):
  File "C:\Program Files\Python34\lib\site-packages\supybot\world.py", line 121, in flush
    f()
  File "C:\Program Files\Python34\lib\site-packages\supybot\plugins\__init__.py", line 271, in flush
    writer.writerow(L)
  File "C:\Program Files\Python34\lib\site-packages\supybot\utils\file.py", line 172, in write
    return self._fd.write(data)
  File "C:\Program Files\Python34\lib\encodings\cp1250.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode character '\u25c4' in position 33: character maps to <undefined>

plugins/__init__.py

@@ -32,6 +32,7 @@ import gc
 import os
 import csv
 import time
+import codecs
 import fnmatch
 import os.path
 import threading
@@ -221,7 +222,7 @@ class ChannelUserDB(ChannelUserDictionary):
         ChannelUserDictionary.__init__(self)
         self.filename = filename
         try:
-            fd = open(self.filename)
+            fd = codecs.open(self.filename, encoding='utf8')
         except EnvironmentError as e:
             log.warning('Couldn\'t open %s: %s.', self.filename, e)
             return

src/utils/file.py

@@ -30,6 +30,7 @@
 
 import os
 import time
+import codecs
 import random
 import shutil
 import os.path
@@ -126,7 +127,8 @@ class AtomicFile(object):
         makeBackupIfSmaller = True
         allowEmptyOverwrite = True
     def __init__(self, filename, mode='w', allowEmptyOverwrite=None,
-                 makeBackupIfSmaller=None, tmpDir=None, backupDir=None):
+                 makeBackupIfSmaller=None, tmpDir=None, backupDir=None,
+                 encoding=None):
         if tmpDir is None:
             tmpDir = force(self.default.tmpDir)
         if backupDir is None:
@@ -135,6 +137,8 @@ class AtomicFile(object):
             makeBackupIfSmaller = force(self.default.makeBackupIfSmaller)
         if allowEmptyOverwrite is None:
             allowEmptyOverwrite = force(self.default.allowEmptyOverwrite)
+        if encoding is None and 'b' not in mode:
+            encoding = 'utf8'
         if mode not in ('w', 'wb'):
             raise ValueError(format('Invalid mode: %q', mode))
         self.rolledback = False
@@ -153,7 +157,7 @@ class AtomicFile(object):
             self.tempFilename = os.path.join(tmpDir, tempFilename)
         # This doesn't work because of the uncollectable garbage effect.
         # self.__parent = super(AtomicFile, self)
-        self._fd = open(self.tempFilename, mode)
+        self._fd = codecs.open(self.tempFilename, mode, encoding=encoding)
 
     def __enter__(self):
         return self