Transport.postJSON() does not respect the host and path variables set on the transport.

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Steps to reproduce:
1. Instantiate a new REST() transport with a custom hostname and port, then 
call setPath() on the transport instance with a custom path.
2. Instantiate a Flickr instance using the 3-parameter constructor that 
includes the transport instance as the 3rd parameter.
3. Call an API that results in the transport's postJSON() method to get called 
(e.g. a signed request for "flickr.photosets.getList")

Expected output:
Should result in a POST to <custom_host>:<custom_port>/<custom_path>

Observed output:
The POST request goes to <custom_host>:<custom_port>/services/rest and it's 
signed for http://www.flickr.com/services/rest.

Transport.postJSON() seems to be using the hard-coded values 
OAuthInterface.URL_REST and OAuthInterface.PATH_REST instead of building the 
URL and using the path field.

What version of the product are you using? On what operating system?
2.0.7

Please provide any additional information below.

This is needed for component testing since we'd like to use a Flickr emulator 
to generate error scenarios that we aren't able to generate with the real API.

Original issue reported on code.google.com by mthom...@gmail.com on 20 Aug 2013 at 12:53