Patch: Show signature state in encrypted messages using pgg

[Sascha Wilde]

When using pgg to decrypt encrypted messages (via
mml2015-pgg-decrypt), gnus shows only 
[[PGP Encrypted Part:OK]]

Regardless if the message was signed or not.  This is bad, as one
could expect the sender to be authenticated when he reads "OK".

The attached patch extends the message a bit, so that it shows the
signature verification result in addition.  With it a encrypted but
unsigned mail shows:
[[[PGP Encrypted Part:OK, Signer: From unknown user]]

cheers
sascha
-- 
Sascha Wilde : "There are 10 types of people in the world. 
             : Those who understand binary and those who don't."