Convert tests to casper API (bug 1045707)

Make screenshot when test fails

Add LC_ALL=en-US to casperjs command

Remove xvfb as this was for phantom < 1.5

Put casper into package.json

Fix syntax nits

Remove callback as we're not using it.

Use simpler globbing thanks @cvan

Fix README
Merge pull request #556 from muffinresearch/casperjs-1.1

Convert tests to casper API (bug 1045707)