#3196: if needed pad a short base64 encoded word before trying to decode.

The RFCs encourage following Postel's law: be liberal in what you accept.
So if someone forgot to pad the base64 encoded word payload to an
even four bytes, we add the padding before handing it to base64mime.decode.
Previously, missing padding resulted in a HeaderParseError.

Patch by Jason Williams.
diff --git a/Misc/ACKS b/Misc/ACKS
index 0347f67..75c3ae7 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -854,6 +854,7 @@
 Gerry Wiener
 Frank Wierzbicki
 Bryce "Zooko" Wilcox-O'Hearn
+Jason Williams
 John Williams
 Sue Williams
 Gerald S. Williams