Limit queue depth

Without dead-lettering yet
Better maxdepth checking
Maxdepth checking with confirms and DLX
Shortcut
Ensure TTL conditionally
Whitespace
Dead-letter persistent messages differently
Remove unused variables
Confirms for HA
Maxdepth argument checking
Inline
Merged default into bug19375
Remove confirm_all
Rename depth to length
Ignore queue depth for maxlen
refactor: disentangle head dropping and publishing
merge default into bug19375
cosmetic
Merged default into bug19375
Update dead-lettering due to queue length limit