test-onedrive fails with Boost 1.59.0

The test-onedrive testcase fails when compiled with Boost 1.59.0

Debugging revealed that an exception was being thrown from OneDriveSession::getObjectByPath(string) because no match was found. This is because the Json::parse( res ) call returns an empty object with no JSON objects. That turns out to be because the boost::property_tree::json_parser::read_json() function throws an exception, which is swallowed by Json::parse(const string&).

The exception is thrown because Boost.PropertyTree 1.59.0 does not allow comments in JSON (which is correct, the JSON spec doesn't allow them either). The JSON document used in the test has lines with comments:

  "parent_id":"folderC", // path: /A/B/C/Right File