Moriarty updates rev 262

[Ian Davis]

I just committed in revision 262:

* replaced references to request objects in httprequest class with
copies of request method, uri, headers and body to reduce size of
cache files
* fixed problem where a conditional GET resulting in a 304 did not
return the cached request
* replaced requests using application/x-turtle with text/turtle
* added store_data method to the store class
* improved labeller's get_prefix method to generate a qname prefix
* added a tophat logo file

However, I noticed that there are broken unit tests from Keith's
checkin on Friday - the new list methods on simplegraph are not
passing their tests