returning false if buffer full for exchange manager

[vincentberenz]

changes are related to the exchange manager:

• exchange manager used previously a segment id and an object id. This was just to only using a segment id, the object id being created automatically.

• functions for adding new commands returns false if the commands were not added because the buffered queue was full

• added some dirty hack that content of empty interprocess queues are purged. This is strange because it should not be possible to remove items from an empty queue. But if this is not done, the programs randomly hang.

• added exchange manager unit tests

[vincentberenz]

addressed the comments and merged