FBC: Can't make package version 3 object in L3v2 core model.

[luciansmith]

It's impossible to create a flux objective and add it to an L3v2 model:

• If you run createFluxObjective(), it gives you an object with a getLevel() of 3, a getVersion() of 2, and a getPackageVersion() of 3. When you call 'setVariableType', it notices that getVersion is 2, and returns LIBSBML_UNEXPECTED_ATTRIBUTE.
• If you create a FluxObjective with FluxObjective(3,1,3), it lets you call 'setVariableType', but doesn't let you call addFluxObjective(), because of the version mismatch to the core SBML object.

I propose that packages in general should never check the core level or version; they should only check the package version. (Perhaps the layout/render functions could check the core level, but even they shouldn't check the core version.) Putting 'version1' in the namespace string turns out to be a terrible idea, but that ship has sailed; at this point, all we can do is just not check it.

For the immediate problem, I say we don't check versions when calling 'addXXX', nor when calling 'setVariableType' for FBC objects, but a more thorough scouring of the code will probably be necessary to check for other packages moving forward.

@skeating @fbergmann Opinions?

[fbergmann]

I agree, checking the packageVersion is definitely sufficient.