BUG: Output vector argument should not be assigned.

Assignment to a required return parameter should not be assigned, and results
in a compilation.  Skip as already is done with the non-parameter arguments
(lines 1650-1662 of GenerateCLP.cxx).

The missing condition is added to the test suite.
Merge pull request #28 from thewtex/return-vector

BUG: Output vector argument should not be assigned.

The code generation assigning parameters to the values passed on the command line (or assigning to their default values) needs to ignore "return parameters" (as they are not set to values on the command line).  Scalar return parameters were handled properly. However, vector parameters are handled separately and that code was missing the conditional to ignore a return parameter.