Until now, those messages would be accumulated and displayed all at
once, when a '\n' was finally emitted by 'guix substitute'. In the
meantime, clients would remain silent.
* guix/status.scm (bytevector-index): Change 'number' parameter to
'numbers' and adjust accordingly.
(build-event-output-port): Pass both #\newline and #\return to
'bytevector-index'.
* tests/status.scm ("build-output-port, daemon messages with LF"): New
test.
