Attmpt to fix https://github.com/ceylon/ceylon-compiler/issues/1475

We should not throw the error when the member obtained by `getMembers()`
is an overloaded version of a Java class constructor (since it can be shared while the corresponding abstraction declaration is not). Just skip it since
`getMembers()` also returns the corresponding abstraction declaration

It seems OK to me, and the spec tests pass, but I prefer you to confirm this is the right thing to do.