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Conflicts:
	agents/newmailnotifier/specialnotifierjob.cpp

Needed for at least Zimbra that doesn't like
having items files named by anything else but
the incidence UID and that redirects. KIO
does not supply the username / password (as
it should), but we have no way to ask the user
for confirmation.

Many thanks to Benjamin Girault for the initial
debug, patch and testing.

BUG: 339634

Conflicts:
	CMakeLists.txt

Conflicts:
	agents/newmailnotifier/specialnotifierjob.cpp

Conflicts:
	accountwizard/providerpage.cpp

Conflicts:
	resources/imap/autotests/testremoveitemstask.cpp
	resources/imap/changeitemsflagstask.cpp
	resources/imap/removeitemstask.cpp
	resources/imap/tests/CMakeLists.txt

Although not specified in RFC, IMAP servers usually have some limit on maximal
length of a command send by clients. This is best visible in case of ChangeItemsFlagsTask,
which would create an insanely long STORE command when user marked as read
thousands of emails at once.

To prevent servers from rejecting our requests, we split large STORE requests
to multiple smaller ones, each of 2000 UIDs at most. 2000 sounds like a good
compromise between not hitting it too often (i.e. users usually mark as read
few emails at once, hundreds at best) and not hitting the server-side limits
(every server out there should handle 2000 UIDs in a request). This number
can be tuned later of course if we find out it's too much/not enough.

REVIEW: 120446
BUG: 339565
FIXED-IN: 4.14.2

Removing emails means appending the \Deleted flag, so RemoteItemsTask is
just a simpler version of ChangeItemsFlagsTask with hardocded flag to append.
To avoid code duplication and make use of flags-related fixes in ChangeItemsFlagsTask,
we can just use that instead of RemoveItemsTask.

REVIEW: 120447
CCBUG: 339565