Instead -J will behave as if it was built without concurrent-output support
in this situation. Ie, it will be mostly quiet, except when there's an
error.
Note that it's not a problem for a filename to contain invalid utf-8 when
in a utf-8 locale. That is handled ok by concurrent-output. It's only
displaying unicode characters in a non-unicode locale that doesn't work.
Commands that want to use it have to run their seek action inside
allowConcurrentOutput. Which seems reasonable; perhaps some future command
will want to support the -J flag but not use regions.
The region state moved from Annex to MessageState. This makes sense
organizationally, and note that some uses of onLocal use a different Annex
state, but pass the MessageState into it, which is what is needed.
It sounds worse than it is. ;)
Some external special remotes may run commands that display progress on
stderr. If git-annex is run with --quiet, this should filter out such
displays while letting the errors through.
Came up with a generic way to filter out progress messages while keeping
errors, for commands that use stderr for both.
--json mode will disable command outputs too.
