Improve testing

[jimmed]

• I want slapdash to be as resilient as possible.
• We are going to be using it in extremely 'hostile' environments (things aren't necessarily what they say they are)
• While we recommend against it, we still support loading individual methods from source, as well as the whole bundle.

So:

• Each test case should be run:
  • with the method from the bundle
  • with the method from source
• Each of the above should also be run with:
  • intact native methods (where applicable)
  • overriden native methods

I propose replacing the outermost describe in each test suite with a describeMethod, which does something like:

natives.capture()
function describeMethod (methodName, suiteCallback) {
  describe(methodName, function () {
    describe('from bundle', function () {
      describe('with native methods', function () {
        suiteCallback(require('../dist/')[methodName])
      })
      describe('without native methods', function () {
        beforeEach(natives.override)
        afterEach(natives.restore)
      })
    })
    describe('from source', function () {
      // ... and again, but imported from ../src
    })
  })
}