Fix spawn*() so it can report errors to the caller

If nopen is not in PATH, noice will briefly print a warning about it
so the user knows.

Also, add NOPENCMD define in noiceconf.def.h to specify the default
plumber program.

1 files changed, 1 insertions, 0 deletions

diff --git a/TODO b/TODO
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+- Support overriding plumber via environment variable