Merge pull request #118 from bdecarne/master

Avoid duplicate Content-Length header in EasyRdf_GraphStore
Add support for passing objects of type DateTime to $graph->add() (fixes #119)
Merge branch 'master' of github.com:njh/easyrdf
Removed test for Content-Length header, this is (now only) set by the HTTP Client class. See #118
Minor correction to comment
Add support for large SPQARQL queries by HTTP POSTing when query is over 2k (fixes #85)
Changed formatting of xsd:dateTime from DateTime::ISO8601 to DateTime::ATOM
Renamed variable from $iso to $atom
Removed use of empty() in Literal.php
Current time/date is now used if no value is passed to new EasyRdf_Literal_Date or EasyRdf_Literal_DateTime object.
Fix for date comparison test on PHP 5.2
Move literal dayatype registration from individual files to EasyRdf_Literal, so that an autoloader can be used
Fix for dumping literal with unshortenable datatype uri (fixes #120)
Added rss:title to the list of properties that label() will check for.
Fix for getting default mime type or extension when there isn't one
Added MIME type and file extension to PHP format registration
Code style fixes
Added rdf:Seq test case into fixture file
Added EasyRdf_Container to help iterate through rdf:Alt, rdf:Bag and rdf:Seq
codestyle