Fixed BooleanFields being coerced null=True in Oracle.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10505 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/__init__.py

@@ -370,6 +370,7 @@ class AutoField(Field):
         return None
 
 class BooleanField(Field):
+    empty_strings_allowed = False
     def __init__(self, *args, **kwargs):
         kwargs['blank'] = True
         if 'default' not in kwargs and not kwargs.get('null'):