[Imps] Test cases for parsing spec

[Robert Sayre]

Just a quick note to say that I unfortunately find myself owning some
testing infrastructure in Mozilla.

On the upside, this does mean that I can make sure an MIT-licensed
test suite with a language-agnostic Expect format will be integrated
into the Mozilla build process.

I don't own the HTML parser, but I suspect that patches will go
smoothly in the presence of a test suite (exceptions will probably
grounds for spec discussion).

-- 

Robert Sayre