Concatenate log msgs when jobs in progress and queue is attempted processing

ie, currently, if there's a long-duration job running and job processing schedule is every minute, logs can fillup with same message at the top "Tried to process queue while other jobs are running".

This adds noise and makes logs less readable. Rather:

- when message about to be added, check for previous message with same format
- update that message, incrementing a counter to show how many times it's been called