Check for key exists before add to info dictionary

[edwardt]

Dictionary is a Set and complains about a duplicate items.
so in methods:
public ContainerResponse GetContainer(string url, string token, string container, Dictionary<string, string> headers, Dictionary<string, string> query, bool full_listing)

and
public AccountResponse GetAccount(string url, string token, Dictionary<string, string> headers, Dictionary<string, string> query, bool full_listing)

it will throw exception if info.ContainsKey(key) not checked before info.add ...