WCS memory leak

The following program leaks memory:

    from astropy.wcs import WCS
    w = WCS()
    while True:
        w.deepcopy()

It also leaks for `.copy()`.

I use a numpy array subclass with an attached WCS object, and this mechanism makes those arrays leak memory whenever a copy/slice/whatever is done on those arrays. It's only a small amount of memory each time, so I didn't notice for a while, but today I encountered a situation where it kills my programs after running for just a few minutes. So this is a serious issue to me.