Resets all HTTP headers, cookies, and LocalFile.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
Resets all the HTTP headers as well as LocalFile to "" (empty string), and clears the Metadata* and QueryParam* properties.
Call this method before creating a new request, so that headers and query parameters from the previous request are not carried over to the next one.