Fix some browser test suites

The load() method used in tests used the ```fs.readFileSync``` API which I shimmed in our tests with a synchronous XHR now.

This gets us for example:
```
level2/html      711/718      99%
```
(up from 0/718)

Haven't tried to enable the others yet.
Nit: Prefer `exports.readFileSync = ...` to reduce the indentation level.