Add __str__ to case insensitive dict. Logging headers for debugging purposes is often necessary, and the currently logging the headers would be using __repr__ which would log the implementation detail of headers, caseinsensitivedict. Adding str lends a more printing and log friendly implementation for case insentitice dict
Fix parenthesis typo
Shorten str for case insensitive dict
Merge pull request #1972 from avidas/response_str

Add __str__ to case insensitive dict