broadcast: starting broadcast halts broadcast checker

[Saxon Milton]

If one of the broadcasts we check is scheduled to start, we end up halting the entire handler. This means that any other broadcast that is schedule to start at a similar time will not get started. Instead, the start of a broadcast could be done using a routine.

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[Saxon Milton]

Merged in dodgy-pointer-use (pull request #240)

broadcast: use routine for broadcast start process

Resolves issue #251

Approved-by: Alan Noble

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