simplify JSON-LD serialization

- Don't use @graph if it's not needed
- Make sure Jena's serialization doesn't use
  graph URI urn:x-arq:DefaultGraphNode

Fixes #197
Minor problem with earl report filenames
Don't test wildcard Accept header (outside spec)
Merge branch 'accept-wild' of github.com:jamesrdf/ldp-testsuite
Merge branch 'master' of https://github.com/spadgett/ldp-testsuite
Merge pull request #199 from jamesrdf/accept-wild

Don't test wildcard Accept header (outside spec)
Merge branch 'master' of https://github.com/w3c/ldp-testsuite