Export is.waive() for extensions to use

[arcresu]

waiver() is an internal detail of ggplot that end-users don't really need to be aware of, but extensions that define new stat_*() or geom_*() functions generally need to be able to check for waivers for the same reason that ggplot itself does.

I find that most extensions I write need to copy the definition of is.waive(), and I'm not alone. Would you consider exporting it for extensions to use?

[teunbrand]

Agreed, this would be good to have available in extensions.
Would you mind adding a news bullet stating that is.waiver() is now exported?

[arcresu]

Done. Though that does raise the question of whether this should be is.waive() or is.waiver(). I got used to the former, but since the class is waiver we could rename it? I'm happy either way.

[teunbrand]

Good point! I think is.waiver() makes more sense in this case then because it has symmetry between the class name and the test function. If you're feeling up for it, you can rename the function and replace all the is.waive() calls with is.waiver() calls, but if you rather not, I'm also happy to do it.

[arcresu]

No problem; rename done.

[teunbrand]

Great, thank you very much for the contribution!