Fix tokenizer test harness to not decode tests multiple times.
Fix tokenizer test harness to not decode tests multiple times.

Given a double escaped test, if it had multiple initial states, the
same test object would be decoded multiple times: this led to bogus
results on every run except the first.

ordbogen/html5lib-python,alex/html5lib-python,dstufft/html5lib-python,mindw/html5lib-python,html5lib/html5lib-python,dstufft/html5lib-python,gsnedders/html5lib-python,alex/html5lib-python,html5lib/html5lib-python,mgilson/html5lib-python,mgilson/html5lib-python,gsnedders/html5lib-python,ordbogen/html5lib-python,html5lib/html5lib-python,dstufft/html5lib-python,mindw/html5lib-python,ordbogen/html5lib-python,mgilson/html5lib-python,mindw/html5lib-python,alex/html5lib-python