When built with concurrent-output 1.9, ssh password prompts will no longer
interfere with the -J display.
To avoid flicker, only done when ssh actually does need to prompt;
ssh is first run in batch mode and if that succeeds the connection is up
and no need to clear regions.
This commit was supported by the NSF-funded DataLad project.
This makes -Jn work with --json and --quiet, where before
setting -Jn disabled those options.
Concurrent json output is currently a mess though since threads output
chunks over top of one-another.
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.
