Fixed bug where Hash#to_param did not order query string parmeters correctly.

The current Hash#to_param method sorts the query string keys after appending "=#{value}" onto the end of the key. This causes incorrect sorting of the query string if the keys have certain non-alphanumeric characters, such as ".". This bug was discovered trying to make AWS API requests via Rails, since AWS requires "." in the query string and also requires that query string parameters be sorted. 
No need to make the nil case explicit. if/unless return nil when they fail to match.