Raise a ValueError if Graph.items is called with a recursive collection

Fixes a bug where, if a graph contains a closed/self-referencing chain
of rdf:rest statements, Graph.items would be caught in an endless loop.
- structured data parser should set the media type explicitly if it does not receive it; added a default keyword argument, too
- Dataset is now a Graph as opposed to a ConjunctiveGraph, though this may change in future
Ensure quads added with addN have contexts that are a graph instance. tests and fixes #299
temporarily ping html5lib to 0.95 for py 2.6/2.7
Merge branch 'master' of https://github.com/RDFLib/rdflib
pointer to update topic of #rdflib on release
minor cleanup
Merge branch 'master' of github.com:RDFLib/rdflib
make conjuctivegraph accept triples or quads for add/remove, preparation work for a fix to #307
Fixing __UNION__, this time in Graph.update

This has already been fixed in Graph.query, but noone thought about
Graph.update.
Setting default graph via URL parameter

SPARQL 1 and 1.1 both know the URL paramter 'default-graph-uri'. It can
is used to set the default graph of a query. Previously, when doing a
query on a context of a Conjunctive graph backed by the SPARQLStore, a
GRAPH clause is injected into the INSERT. Modifying the query is not
robust. Now, the default-graph-uri is set while leaving the query
unmodified.

The same is possible in SPARQLUpdateStore with the parameter
using-graph-uri, but it is not used by this commit, because it does
not work with my SPARQL endpoint.
there's no more reunification branch
include running tests for coveralls-ci branch

this is just for the time of setting up coveralls integration
coveralls ci, badge in readme. resolves #308

this squashes the several trial and error attempts to get the integration
running from the coveralls-ci branch into a single commit, as that stuff
is mostly rdflib unrelated.
make code coverage main guard exclusion more tolerant
Merge branch 'master' of https://github.com/RDFLib/rdflib

Conflicts:
	rdflib/graph.py
enabled irc notifications for #rdflib
Use ConjunctiveGraph in rdfpipe to support parsing and serialization of datasets
Do not add extra namespace bindings in rdfpipe (clutters output unnecessarily)
pyRdfa: Took care of an encoding issues with HTML literals and also with XML Literals (the usual unicode vs. encoding problem in Python2:-(