fix --all to include not yet committed files from the journal

fix --all to include not yet committed files from the journal

Fix bug caused by recent optimisations that could make git-annex not see
recently recorded status information when configured with
annex.alwayscommit=false.

This does mean that --all can end up processing the same key more than once,
but before the optimisations that introduced this bug, it used to also behave
that way. So I didn't try to fix that; it's an edge case and anyway git-annex
behaves well when run on the same key repeatedly.

I am not too happy with the use of a MVar to buffer the list of files in the
journal. I guess it doesn't defeat lazy streaming of the list, if that
list is actually generated lazily, and anyway the size of the journal is
normally capped and small, so if configs are changed to make it huge and
this code path fire, git-annex using enough memory to buffer it all is not a
large problem.