Fix bsddb.db.DBError derived exceptions so they can be unpickled.

Also adds some backwards compatibility when compiling _bsddb.c on earlier
python versions (needed for pybsddb).
diff --git a/Misc/NEWS b/Misc/NEWS
index bfac78c..266b6c9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -15,6 +15,8 @@
 Extension Modules
 -----------------
 
+- Fix bsddb.db.DBError derived exceptions so they can be unpickled.
+
 Library
 -------