Revise description of the POST method

[mnot@…]

The description of POST was broadened over time, and is not clear. It is clarified by the following changes in Section 9.5:

The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line.

should be:

The POST method is used to request that the origin server accept the entity enclosed in the request as data to be processed by the resource identified by the Request-URI in the Request-Line.

Likewise:

The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI. The posted entity is subordinate to that URI in the same way that a file is subordinate to a directory containing it, a news article is subordinate to a newsgroup to which it is posted, or a record is subordinate to a database.

should be:

The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI.

[fielding@…]

Fixed in [78]