fix a typo
Return 2 from VSUB_run() when the sub process dies with a signal.

Fixes a regression from 33e6fe71743059b912d2b00cdbc08196b003e440

Fixes #1585
panic with INCOMPL() rather than exit(4)

Fixes #1583
Add an informative warning when only starting the master process in daemon mode

Fixes #1580
make the update interval a double to allow values < 1
should ignore return value of usleep()