respect Error.stackTraceLimit, pass JS Array of CallSite objects to Error.prepareStackTrace, improve CallSite object itself
clean up error_constructor a bit, hide _frames in metatable instead
fix bug where first frame got dropped/ignored as `this` paramter when making JS Array, and off-by-one error introduced trying to compensate
implement the trivial CallSite getters
check .name instead of .type in tests, now they pass under v8 too
Error properties vs. prototype fixup/simplification, and fixes #457