Fix #3: test ">" in script data double escaped dash state

This test is written to ensure that it is treated differently to how
it is in the script data double escaped dash dash state, as this was
the bug html5lib-python used to have.
Merge pull request #36 from gsnedders/fix-3-script-data-double-escaped-dash-state

Fix #3: test ">" in script data double escaped dash state; r=jgraham