#1466065: add validate option to base64.b64decode

Patch by Neil Tallim.  This provides a mechanism for module
users to achieve RFC 3548 compliance in the cases where ignoring
non-base64-alphabet input characters is *not* mandated by the RFC that
references RFC 3548.
diff --git a/Misc/NEWS b/Misc/NEWS
index a887faf..2ff7247 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -63,6 +63,9 @@
 Library
 -------
 
+- Issue #1466065: Add 'validate' option to base64.b64decode to raise
+  an error if there are non-base64 alphabet characters in the input.
+
 - Issue #10386: Add __all__ to token module; this simplifies importing
   in tokenize module and prevents leaking of private names through
   import *.