error: Clean up errors with embedded newlines (again)

error: Clean up errors with embedded newlines (again)

The arguments of error_report() should yield a short error string
without newlines.

A few places try to print additional help after the error message by
embedding newlines in the error string.  That's nice, but let's do it
the right way.  Commit 474c213 cleaned up some, but they keep coming
back.  Offenders tracked down with the Coccinelle semantic patch from
commit 312fd5f.

Cc: Laszlo Ersek <[email protected]>
Cc: Pavel Fedin <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Laszlo Ersek <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Signed-off-by: Markus Armbruster <[email protected]>