suggest when user may want annex.stalldetection

When annex.stalldetection is not enabled, and a likely stall is detected,
display a suggestion to enable it.

Note that the progress meter display is not taken down when displaying
the message, so it will display like this:

	0%    8 B                 0 B/s
	  Transfer seems to have stalled. To handle stalling transfers, configure annex.stalldetection
	0%    10 B                0 B/s

Although of course if it's really stalled, it will never update
again after the message. Taking down the progress meter and starting
a new one doesn't seem too necessary given how unusual this is,
also this does help show the state it was at when it stalled.

Use of uninterruptibleCancel here is ok, the thread it's canceling
only does STM transactions and sleeps. The annex thread that gets
forked off is separate to avoid it being canceled, so that it
can be joined back at the end.

A module cycle required moving from dupState the precaching of the
remote list. Doing it at startConcurrency should cover all the cases
where the remote list is used in concurrent actions.

This commit was sponsored by Kevin Mueller on Patreon.

Annex/Concurrent.hs

@@ -19,7 +19,6 @@ import Types.Concurrency
 import Types.CatFileHandles
 import Annex.CheckAttr
 import Annex.CheckIgnore
-import Remote.List
 
 import qualified Data.Map as M
 
@@ -72,11 +71,6 @@ forkState a = do
  -}
 dupState :: Annex AnnexState
 dupState = do
-	-- Make sure that some expensive actions have been done before
-	-- starting threads. This way the state has them already run,
-	-- and each thread won't try to do them.
-	_ <- remoteList
-
 	st <- Annex.getState id
 	-- Make sure that concurrency is enabled, if it was not already,
 	-- so the concurrency-safe resource pools are set up.