ACTION-682: Write a proposal on the HEAD request handling

This is my proposed text for the treatment of HEAD requests from the clients.  This would go somewhere in section 3.1.2: 


HEAD requests from clients  


Clients can issue HTTP HEAD requests in order to determine if a resource is of a type and/or size that they are capable of handling.  A proxy  may  convert a HEAD request into a GET request if the response body is required to allow the proxy to analyze the response content  to determine the characteristics of the transformed response that it would return if the client issued a GET request.   Where this occurs, the proxy should  (subject to HTTP cache directives) cache the response that it receives so that if the client immediately follows the HEAD request with a GET request for the same URI, the proxy does is not required to send a second GET request to the server. 


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Martin