Include real diff.js in browser build

Fixes https://github.com/metaskills/mocha-phantomjs/pull/30
Add instanceof check for inheriting from Error

* instanceof is faster so put it first:
  http://jsperf.com/error-instanceof-performance
Use proper Object.create-style inheritance in browsers.
Minor fix to HTML reporter display.

Previously the HTML reporter displayed 'pre' blocks with display set
to 'inline-block', however given a wide enough screen, when a test
fails and you click the h2, the code snippet will display beside the
error output, as opposed to below it which would look more
consistent. This commit fixes this styling.
Remove unused requires, vm and exec
Merge pull request #708 from juzerali/remove-unused-vars

Remove unused requires, vm and exec
Merge pull request #691 from jfirebaugh/diff

Include real diff.js in browser build
Merge pull request #701 from gregrperkins/error_inheritance

Add instanceof check for inheriting from Error
Merge pull request #703 from domenic/inheritance

Use proper Object.create-style inheritance in browsers.
merge
fix replay button css
Release 1.8.0
Bump component.json version.
Update license year.
fix .bail() arity check causing it to default to true
Merge pull request #709 from paulmillr/patch-1

Bump component.json version.
Release 1.8.1
build