Expression rule for current node and fix getting unique nodes

[lar-dragon]

Rules with expressions allow select nodes by name and content in Jayway JsonPath implementation. for example:

[
 { "a": { "c": 1, "d": 1 }, "b": { "c": 1, "d": 2 } },
 { "a": { "c": 2, "d": 3 }, "b": { "c": 2, "d": 4 } }
]

rule $..a[?(@.c==2)] selects

[ { "c" : 2, "d" : 3 } ]

This changes add similar behavior and allow getting unique nodes with values by references. The following code becomes valid:

$jsonStore = new JsonStore([
 [ "a"=>[ "c"=>1, "d"=>1 ], "b"=>[ "c"=>1, "d"=>2 ] ],
 [ "a"=>[ "c"=>2, "d"=>3 ], "b"=>[ "c"=>2, "d"=>4 ] ]
]);
// set "d" to 5 only for "a" node witch field "c" equivalent 2
$jsonStore->get('$..a[?(@.c==2)]', true)[0]['d'] = 5;