Support race conditions B.7, B.9, B.10 and Q8

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RCSe 1.2.2 and 5.1 spec describes 3 race conditions for terminating chat 
session. Moreover, the implementation guidelines clarifies another race 
condition in Q8. All these changes are relevant for the class 
TerminatingOne2OneChatSession (and their derived classes 
TerminatingStoreAndForward*Session).
If wanted I could provide a fix.

Original issue reported on code.google.com by andreas-...@telekom.de on 21 Feb 2014 at 4:26