Support "old subject" variable in vacation

[PF4Public]

At first I thought to file this as an issue here, but later I thought what could be easier than adding
"if header :matches "Subject" "*" { set "subjwas" ": ${1}";}" to the vacation template and adding a pull request myself. Well, it turned out "would that it were so simple".
So my questions are:

1. Is it useful as a feature to have some kind of checkbox which adds this to vacation so that users may use {$subjwas} in their response texts?
   You can tell that this could be easily achieved by adding specific rule in filters, but that's more frightening for common users, who might prefer having a checkbox for that.
2. As I mentioned, I thought to implement this myself, but stumble across several issues:
   a) Vacation only checks for its very own single rule, but as far as I understand this particular line should have it's own rule, so that vacation_rule() should be significantly rewritten to accommodate for two rules. Is that true?
   b) Having added this rule as it is, I'm afraid it will fail to add "variables" as requirements. Is that true?
   c) May I ask someone to implement this? :)

[alecpl]

RFC5230: 5.3. Subject
Users can specify the Subject of the reply with the ":subject"
parameter. If the :subject parameter is not supplied, then the
subject is generated as follows: The subject is set to the characters
"Auto: " followed by the original subject. An appropriate fixed
Subject, such as "Automated reply", SHOULD be used in the event that
:subject isn't specified and the original message doesn't contain a
Subject field.

What's wrong with not specifying :subject, so system uses "Auto: "? Isn't that working on your system? Or you want the original subject in the response text?

[PF4Public]

I'd prefer prefix subject with more meaningful text, such as "On vacation: ", "Outer meeting: " as well as using native language, rather than English.
For instance, Exchange handles auto-responses that way and they look nicer compared to mere "Auto: "
To be honest, I didn't try omitting Subject completely, so that my system might properly generate "Auto: " subject, but that's not what I want.

[Ratedev]

+1 for this feature request

[vendoremo]

+1 for this feature request

html support would also be nice here

another problem is that if field "reply-to" is not empty, auto-response is send to "from" e-mail anyway, usually to no-reply e-mail type in this situation