Doesn't work on loading

Hello,

I'd like tu use ngHelperBusy without promises and on loading of AngularJS.

However, the method `$busy.beBusy();` doesn't work because of the `ngHelperBusy` directive is not yet available from the `run` method of AngularJS.

[jsfiddle](http://jsfiddle.net/r0d97axf)

I 'm going to do a PR.

Bye!
