Avoid redefining `toJSON` if already present.#3

Open

coiscir wants to merge 2 commits intoAVVS:masterfrom

coiscir:avoid-override

Commits on Apr 4, 2016

Avoid replacing existing `toJSON` definitions.
coiscir
committed

Commits on Apr 5, 2016

Revise to exit module if `toJSON` is already defined.
coiscir
committed