SetFixedTest: add two new test cases
FixedNumericTest: add new test case

Setting the value of a fixed parameter is legal if and only if
the value matches the fixed value.
Added ExtendScopeTest
ExtendScopeTest: add more tests

Added
- circularExtensionsAreLegalButInvalid
- serialExtensionIsValid
- serialDelayedExtensionIsValid
- parallelExtensionIsValid
- intersectingDesignsAreLegal
- extendingSelfIsLegal
- originalParameterTakesPrecedence