desc: reject non-deterministic secondary indexes (#578)
tests:

  - cd: r.db('test').table_create('578')
    def: tbl = r.table('578')

  - js: tbl.index_create("578", function(rec){return 1})
    py: tbl.index_create("578", lambda rec:1)
    rb: tbl.index_create("578") {|rec| 1}
    ot: ({'created':1})

  - js: tbl.index_create("578", function(rec){return 1})
    py: tbl.index_create("578", lambda rec:1)
    rb: tbl.index_create("578") {|rec| 1}
    ot: 'err("RqlRuntimeError", "Index `578` already exists.", [])'

  - js: tbl.index_drop("578")
    py: tbl.index_drop("578")
    rb: tbl.index_drop("578")
    ot: ({'dropped':1})

  - js: tbl.index_drop("578")
    py: tbl.index_drop("578")
    rb: tbl.index_drop("578")
    ot: 'err("RqlRuntimeError", "Index `578` does not exist.", [])'

  - cd: r.db('test').table_drop('578')
