ability to have different test compilation parameters to general compilation parameters

when we stopped doing per goal compilation because of its verbosity, we decided anything that had a different meaning in different mojos within a plugin would need a different parameter name. The compiler plugin slipped through this - specifically the compilation parameters for tests.

What we probably want is to be able to specify the test parameters separately, defaulting to the normal compilation parameters, and then the general defaults.

I think this should depend on us first splitting the compilation parameters into a separate component however so that they can be different depending on whether it is a java compiler, c# compiler, etc.