ACK HANDLING
------------
If there are no remote reliable reader endpoints the new Cache Changes
are immediately ACKed/removed from the HC.
Internal Global ACK SN is set to SEQUENCENUMBER_UNKNOWN, and
only initialized on first reliable remote reader endpoint.
If all remote reliable reader endpints are unmatched the internal Global
ACK SN is set to SEQUENCENUMBER_UNKNOWN and all Cache Changes are
ACKed/removed from the HC.
PUSH MODE
---------
Historical DATA is no longer send on remote endpoint match, if PUSH mode
is FALSE.
TESTBENCH
---------
Level 1 Test2 of rtps_writer was split into 2 tests.
97e55ff623