feat(angular.isRegExp): check object type for regular expressions

[bripkens]

In order to fix #2685, we need to differentiate between regular
expression objects and other types. Angular could expose a public
function 'angular.isRegExp' through which this could be done.

This serves as a preparation for a follow-up pull request for a change to angular.equals (which will fix #2685).

[bripkens]

This is actually a follow up to pull request #2715.

CLA is signed.

[petebacondarwin]

@bripkens - I think that #2685 can be "fixed" by creating a private isRegExp method. Then we can worry about whether to expose this as a public AngularJS API afterwards. It is easier to get private methods merged, since we don't need to worry so much about supporting them going forward. There are a number of such methods already hiding in Angular.js, such as isArrayLike.

[bripkens]

If I change the isRegExp method to be private, then it will effectively not be a feature (I have no problem with this, my intention was only to fix the issue). This would also imply that the previous PR would have been sufficient, if I had removed the exposing part. So please clarify how you wish to handle this.

[petebacondarwin]

Sorry to mess you around. I didn't realise in the previous PR that you were relying on your new public API for the fix.
I'll fix up and merge your previous PR.

[petebacondarwin]

CI server problems ... http://ci.angularjs.org/job/angular.js-pete/174/console

[IgorMinar]

I landed this as 724819e and a357649 (stable branch)

thanks!