Issue #6268: More bugfixes about BOM, UTF-16 and UTF-32

 * Fix seek() method of codecs.open(), don't write the BOM twice after seek(0)
 * Fix reset() method of codecs, UTF-16, UTF-32 and StreamWriter classes
 * test_codecs: use "w+" mode instead of "wt+". "t" mode is not supported by
   Solaris or Windows, but does it really exist? I found it the in the issue.
diff --git a/Misc/NEWS b/Misc/NEWS
index 013d598..4bb8e46 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -31,8 +31,9 @@
 
 - Issue #3924: Ignore cookies with invalid "version" field in cookielib.
 
-- Issue #6268: Fix seek() method of codecs.open(), don't read the BOM twice
-  after seek(0)
+- Issue #6268: Fix seek() method of codecs.open(), don't read or write the BOM
+  twice after seek(0). Fix also reset() method of codecs, UTF-16, UTF-32 and
+  StreamWriter classes.
 
 - Issue #5640: Fix Shift-JIS incremental encoder for error handlers different
   than strict