Constructors are incompatible with extends keyword

[samskiter]

If schema A extends schema B and schema A has properties X,Y and Z and schema B has properties L,M and N and includeConstructors is set to true, the constructor of B correctly has arguments for L, M and N but the constructor of A only has arguments for X,Y and Z.

I would expect A to have LMNXYZ in its constructor.

Looking at the code, this looks non-trivial to fix.

[joelittlejohn]

Closed by #558