I implemented this this afternoon. See changeset: 14abd0a67207

I did not change the default options so quoted_text=yes and keep_body=no

Config descriptions:

 "keep_quoted_text", "yes",
            "Keep email citations when accepting messages.\n"
            "Setting this to \"no\" strips out \"quoted\" text\n"
            "from the message. Setting this to \"new\" keeps quoted\n"
            "text only if a new issue is being created.\n"
            "Signatures are also stripped.",

"leave_body_unchanged", "no",
            "Setting this to \"yes\" preserves the email body\n"
            "as is - that is, keep the citations _and_ signatures.\n"
            "Setting this to \"new\" keeps the body only if we are\n"
            "creating a new issue.",