Display error messages that come from git-annex-shell when the p2p protocol
is used, so that diskreserve messages, IO errors, etc from the remote side
are visible again.
Felt like it should perhaps use outputError, so --json-error-messages would
include these, but as an async IO action, it can't, and this would need
MessageState to be converted to a tvar. Anyway, when not using p2pstdio,
that's not done; nor is it done for stderr from external special remotes
or other commands, so punted on the idea for now.
This commit was sponsored by mo on Patreon.