Insane memory usage in vector

[bgamari]

This test case can easily grow the heap to fill my entire 8GB physical addressing space with both ghc 7.0.3 and ghc 7.4.1. This despite the fact that the original vectors themselves are only 8MB in size and only supposedly non-copying calls are being made. Commenting out either of the prints at the end returns things to sanity. I'm unsure of whether this should be

Presumably the case could be simplified a bit, but this was my first cut at paring it down.

[bgamari]

Reduced test case

[bgamari]

Even smaller test case

[rl]

This is a bug in vector, takeWhile and dropWhile both copy despite what the docs say. I created a  ticket. Thanks for spotting this.