Without this increment, a message could be incorrectly freed in rare
circumstances.

context->state was being overwritten when websockets clients
attempted to disconnect, leaving them in limbo. This has been fixed.

Thanks to FeelyChau.

Prevents busy loop after e.g. writing a large message when using TLS.

Thanks to Dave Sellars.

Thanks to Ed W.

When using CMake it wasn't possible to use libwrap due to a
configuration error. This has been fixed.

Thanks to Markus Rathgeb.

The bridge_attempt_unsubscribe option has been added, to allow the sending
of UNSUBSCRIBE requests to be disabled for topics with "out" direction.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=456899

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=454852

Thanks to Paolo Patierno.

Store a DB wide array of bridges. There shouldn't be many of them, so
iterating/searching isn't a problem. Saves 56 bytes in the client
struct.

Also frees messages from the message store after removing...

This removes the need for *store_clean*.

Comes at the expense of increased memory usage. This could be countered
by using a hash just for loading (increased memory usage during loading,
reduced afterwards) but this approach does allow the immediate removal
of messages from the store.