[Users] Append message for mbox file

[Johan Vromans]

On Wed, 15 Apr 2015 23:20:54 +0200
Johan Vromans <jvromans at squirrel.nl> wrote:

> Thanks for the tip!

Unfortunately, the plugin appends the new messages with an incorrect 
"From " separator line, so they are not seen by (some) mail tools.

RFC#4155 defines the mbox format, and the "From " line must have the UNIX
'ctime' formatted UTC date. So it should be:

  From - Wed Apr 15 22:04:35 2015

instead of what is used currently:

  From - Thu 16 Apr 2015 00:04:35 CEST

-- Johan