[fetchmail] Patch for IMAP idling where idling is unsupported

[Chris Boyle]

Here's a patch I've written: where IDLE is unavailable, it uses periodic
NOOP commands instead (every 28 seconds). Important behavioural change:
the option "idle" will now always result in *some* form of idle. I think
I read somewhere that some servers will unilaterally send status updates
if you just hold the connection open, i.e. NOOPs would be unnecessary,
but that doesn't seem to be the case anywhere I've tried. In any case,
this patch copes with updates both as a response to the NOOPs and
unilaterally sent between them. It functions exactly like normal idling
(N.B. like normal idling, it is single-folder only), and hopefully
includes all the appropriate changes to the documentation. Enjoy. :-)

http://cmb.is-a-geek.org/downloads/fetchmail-6.2.2+noopidle.diff.gz

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