Changes

Summary

1. Putting the exception to nil when clearing debug sessions (details)
2. Clearing debugger model objects referencing debugger exceptions (details)

Commit c6894215b749656debb186fdb6c42db83aec00e1 by steven.costiou Putting the exception to nil when clearing debug sessions
	src/Debugger-Model/DebugSession.class.st (diff)
	src/Debugger-Model-Tests/DebuggerModelTest.class.st (diff)
Commit 8d1415f514269004c326b4dd94083417e6176915 by steven.costiou Clearing debugger model objects referencing debugger exceptions
	src/NewTools-Debugger/StDebuggerActionModel.class.st (diff)