The Grand QUnit Split of 2013

Order is mostly preserved, a few changed had to be made (otherwise
we had to create a core-before.js and core-after.js)

- Prototype split
  This used to be in the middle after Test and Assert. It is now
  right after QUnit is first defined.
  So instead of things becoming globals depending on whether
  they're before or after the prototype split, they now become
  globals depending on whether they use QUnit or
  QUnit.constructor.prototype (some parts of the code used this
  already). Removed the, now redundant, comment about the order
  in assert.js (issue #341)

- Test
  Was close to the top inside core, this is now in its own
  modudle after core.
  No side effects (constructor is still hoisted, prototype now
  assigned later, neither is used until the load event).

- Assert
  Was close to the top inside core, this is now in its own
  module after core and Test.
  Removed the `assert` property from the `extend(QUnit, { .. })`
  in core because that now too early (assert is undefined).
  Moved the assignment to assert.js

- Export
  Due to the reliance on position of the prototype split, the
  export for browser globals was somewhere in the middle and
  the one for CommonJS modules on the bottom. They are now both
  at the bottom.

Build process:

- Based on the build process of jQuery and jQuery UI.

Clean up:
- gitignore: Alphabetized.
- gitignore: 'dist/' was already in there apparently, removed
  redundant slash (matching jQuery).
- package.json: Match order of properties with jQuery.
- package.json: Removed 'contributors' property.
- grunt: Removed old build-git task, like jquery, we don't
  include the git hash. Instead we have 'pre' in the version and
  an exact timestamp.
- src: Simplified file headers to be more like jQuery and made
  them match between js and css.

Fixes #378.