gnus-alias integration bug

[Ian Kelling]

gnus-alias allows you to set your identity based on the headers in the
message you are replying. This is an essential feature in a mail client
for me, I want to automatically reply as the person an email was sent to
for certain addresses. This does not work in notmuch. gnus sets the
variable message-reply-buffer when it sets up a message, which
gnus-alias uses to go grab headers. It creates a buffer named
*gnus article copy* which contains all the headers and the message body. It seems notmuch does not set this
variable when it sets up a reply.

Here is an example of a rule needed to do this.

(setq gnus-alias-identity-rules
        (quote
         (("work"
           ("to" "work at example.com" previous)
           "workidentity"))))