Add threading headers to page change notification mails

[glensc]

configurable with $conf['mailthreads'] (default on)

old patch import:
http://git.pld-linux.org/?p=packages/dokuwiki.git;a=history;f=dokuwiki-mailthreads.patch

[michitux]

I think this could be good for mail clients which don't automatically thread mails (like gmail). I could only see one issue: this will break when you edit the page yourself in between two edits by other users. Maybe it would also be good to make the message id a bit more unique, but I'm not sure if this is actually needed (and I also don't know if this format is correct).

[glensc]

i don't see how it could go wrong, if for each edit mail is sent out the and message id is page $rev, it will just magically match. there is no user information in the id, just pagename?rev=$rev@wiki.url

[michitux]

The problem is that you don't get emails for your own edits when you are subscribed to a page, which means there is one message id missing and the mail client can't find the thread anymore.

[glensc]

ah, okay. i'm using $conf['notify'] to receive all mails, therefore i haven't noticed this behaviour.

i can't think of solution for this case how to avoid it. and it's not exactly breakage, just you'll get different mail threads in your mail client.

[splitbrain]

I like this. I don't think we need a config option for this though. It wouldn't hurt anyone, right?

[glensc]

i added it just to be safe, because i don't know (can't even imagine) what could go wrong.

should i remove the config part from the PR?

[splitbrain]

Yes, let's get rid of that.

[glensc]

uh, there's media notify too, i'll commit change for that as well

[splitbrain]

This should be merged with the changes of #125

[michitux]

Implemented/merged in 10eac67.