Automatic merge from submit-queue

Fix spacing in usage_from_stdin and info_from_stdin (issue #24186).

If "a" is a bash array, then the syntax to append the contents of $line as a
new element to the array is a+=("$line"), not messages+=$line

Using the former syntax just seems to append to the first element, creating a
long string and thus losing newline information.

Fixing this allows us to drop some empty lines from invocations of
usage_from_stdin.