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

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

 - cd: r.expr(a)
   ot:
     py: err('RqlDriverError', 'Nesting depth limit exceeded', [])
     js: err('RqlDriverError', 'Nesting depth limit exceeded', [])
     rb: err('RqlRuntimeError', 'Maximum expression depth of 20 exceeded.', [])

 - cd: r.expr({'a':{'a':{'a':{'a':{'a':{'a':{'a':{}}}}}}}}, 7)
   rb: []
   ot: err('RqlDriverError', 'Nesting depth limit exceeded', [])

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