Manage debug mode with more precision

[buxx]

For now, we permit to display or not a traceback when context is in debug mode. We should permit more flexible:

When add exception handling with a decorator, or directly with context:

• Permit to allow or not a message extracted from exception.

By default, behavior should be: Not in debug mode, and no precision about message: no message When debug mode is activated: extract message from exception. When no debug mode but allow message from exception: extract message from exception.

This is important to permit to not expose internal sensitive informations when error.