Expose only the specified UI in the browser

[jugglinmike]

I'm happy to add tests for this, but it doesn't look like there are any tests for the browser build--is this the case?

Commit message:

When instantiated in the browser, Mocha registers the "BDD-style"
interface. Since an explicit call to the browser-specific mocha.ui is
required, the original registration is invalid. Prevent that UI from
reacting to the pre-require event (and exposing its API).

[jugglinmike]

@visionmedia Does this look okay to you? Is there anything else I can do to help get it merged?

[jugglinmike]

@travisjeffery Looks like TJ's a little busy. Would you mind reviewing this?

[travisjeffery]

it's not clear why's this change is needed?

[jugglinmike]

If you run Mocha in the browser today, it will always expose the BDD style interface.

For example, in an environment that states: mocha.setup({ ui: 'tdd' });, the describe and it functions will be defined globally in addition to the suite and test functions.

[travisjeffery]

just tested this by switching this line https://github.com/visionmedia/mocha/blob/master/test/browser/index.html#L8 to use the tdd interface and describe wasn't defined.

[jugglinmike]

@travisjeffery That is the intent of this pull request. When you specify the "tdd" interface, describe should not be defined.

[travisjeffery]

no i knew the intent, i thought i was testing it without your change and still seeing that expected behavior. all good now

[jugglinmike]

Ah, I see. Thanks for reviewing!