[Users] "Go Offline" button on connection error popup

[Bernd Eckenfels]

I am using Claws with some IMAP4 accounts. They are set to
automatically retrieve mails every few minutes. This is a notebook, and
when I roam or enable a VPN it happens that the network connection to
my IMAP servers is not available.

There is a setting for error popups. If I disable this (which would be
my preference) then Claws hangs in all kind of situations. Instead of
going into "error" state (using offline or error messages depending on
waht is available) it seems to try synchronously to connect. Would be
better if if tries in the background (like Outlook).

So currently I have the error popup turned on (which is a bit annoying
if it pops up a few minutes after you dialed into some VPN or moved out
of WLAN, but OK. However there is no easy way to dismiss the error and
make Claws stop retrying. It would help if there is an "Go Offline"
button in addition to "Close" and "show log". That button should set
Claws into OFfline mode (stopping the pollings from retrying). This
switching into Offline mode should of course be done without syncing
(unlike the normal offline button). Would that be a good improvement?

Bernd