More completely validate nulls and arrays.

For nulls, check validations common to any type via validateSchema()
and validateCommon().  Also, do not check "type" if it is not declared
in the schema.

For arrays, also call validateSchema()
Merge pull request #5 from tolsen/have-nulls-and-arrays-validateSchema

More completely validate nulls and arrays.
Merge remote-tracking branch 'sigu-399/master' into patternProperties-are-not-additionalProperties