Set mta_version to "unknown" if {v} is unset

[badzong]

No description provided.

[petarb]

On Thu, Sep 04, 2014 at 11:33:03PM -0700, Manuel Badzong wrote:

I suggest testing for v and if unset, set mta_version to "unknown".

There are 3 MTAs that implement the Milter interface:

* Sendmail
* Postfix
* Postoffice (last release Jan 2011)

So I counter-suggest that mopher tests for {v} and, if unset, sets
mta_version to Sendmail. Because that's what you'll assume anyway
when assigning macro_table in milter_macro_lookup().

We also emulate the Sendmail received header.