initial tests of Array.prototype.splice requiring settable "length"

add test of object with only "length" getter

This is a start on the questions raised in #84.  Contrary to my claim there, I am currently seeing a fail in node / v8 on 
S15.4.4.12_A6.1_T2.js
I think you meant to write: `Array.prototype.splice.call(a, 1, 2, 4)`