Set literal references are not evaluated correctly

[tsandall]

If a set literal is referred to with a lookup value containing references to base documents, the evaluation is incorrect. Specifically it will fail because the lookup value will not have embedded references resolved. As a result, the lookup is performed with the reference itself contained in the lookup value, e.g., in pseudocode: set.contains(["a",1,data.foo[2]) instead of set.contains(["a",1,<value-referred-to-by-data.foo[2]).

For example, below pair1 contains a reference data.foo[2] which refers to a string value in the x.json file.

(master)torin:~/go/src/github.com/open-policy-agent/opa$ ./opa_darwin_amd64 run ~/x.json
OPA 0.2.1-dev (commit f56ae0d, built at 2016-11-14T22:07:08Z)

Run 'help' to see a list of commands.

> v = {["a","b"],["c","d"]}
> x = "d"
> pair1 = [data.foo[2], x]
> pair1
[
  "c",
  "d"
]
> v[pair1]
undefined

But lookup values that only contain ground values are fine:

> pair2 = ["c", "d"]
> v[pair2]
true

As are lookup values that contain references to virtual docs:

> y = "c"
> pair3 = [y, x]
> v[pair3]
true

As are lookup values that contain variables with bindings:

> a="c", b="d", pair4=[a,b], v[pair4]
+-----+-----+-----------+
|  a  |  b  |   pair4   |
+-----+-----+-----------+
| "c" | "d" | ["c","d"] |
+-----+-----+-----------+

[tsandall]

Also, there's an issue with sets embedded inside other collections:

OPA 0.2.1 (commit b3f62a1, built at 2016-11-23T16:33:13Z)

Run 'help' to see a list of commands.

> x = [{[1,2], [3,4]}], y = [3,4], x[i][y]
false