MailNotifier: use mime types for log file attachments?

[spurkis]

Some mail programs have trouble guessing what's in the log file attachments of buildbot's MailNotifier? emails. I'd like to be able to set the mime type & extension of a logfile without having to subclass. I also think the stdio logs should be attached as text files by default.

[spurkis]

Obviously stdio logs are already attached as text, I should qualify that: ".txt", mime type text/plain.

I've also been adding html logs, and found I had to explicitly include the ".html" as the logfile name. I was thinking, if we stored the mime type of the logfile then the notifier plugins could use it to do whatever they like (such as adding extensions, setting mime-type, etc).

[dustin]

Sounds good. Patch?