#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
diff --git a/Misc/NEWS b/Misc/NEWS
index a523b8f..dcf2b62 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -37,6 +37,9 @@
 Library
 -------
 
+- Issue #3196: email header decoding is now forgiving if an RFC2047
+  encoded word encoded in base64 is lacking padding.
+
 - Issue #9444: Argparse now uses the first element of prefix_chars as
   the option character for the added 'h/help' option if prefix_chars
   does not contain a '-', instead of raising an error.