Scenario with output parameters

This patch allows to use output parameters in scenarios.
For scripts calling a scenario this was not documented but heavily used if you look at the acceptance tests.
Now this feature can also be used for decision tables. In addition you can now declare the output parameters of a scenario in the header which makes them more readable.
See the new suite FitNesse.SuiteAcceptanceTests.SuiteSlimTests.ScenarioTestSuite for details.

Only to support symbol assignments in decision tables implemented with a scenario a new library function is required in the slim client. For the java client this has been added. For other slim client you need to add them. See the  FitNesse.UserGuide.WritingAcceptanceTests.SliM.SlimProtocol for the new function.

To support in future releases also symbol assignments in Table Tables and Query Tables some more functions have been added already.

Finally if an unknow table type is given in a test this is now flagged as error and not as fail.