desc: Regression tests for issue #1133, which concerns circular references in the drivers.

tests:
 - def: a = {}
 - def: b = {'a':a}
 - def: a['b'] = b

 - cd: r.expr(a)
   ot:
     cd: err('ReqlDriverCompileError', 'Nesting depth limit exceeded.', [])
     rb: err('ReqlDriverCompileError', 'Maximum expression depth exceeded (you can override this with `r.expr(X, MAX_DEPTH)`).', [])

 - cd: r.expr({'a':{'a':{'a':{'a':{'a':{'a':{'a':{}}}}}}}}, 7)
   ot:
     cd: err('ReqlDriverCompileError', 'Nesting depth limit exceeded.', [])
     rb: err('ReqlDriverCompileError', 'Maximum expression depth exceeded (you can override this with `r.expr(X, MAX_DEPTH)`).', [])

 - cd: r.expr({'a':{'a':{'a':{'a':{'a':{'a':{'a':{}}}}}}}}, 10)
   ot: ({'a':{'a':{'a':{'a':{'a':{'a':{'a':{}}}}}}}})