Faster functions for nub, intersect, union

[flip111]

Could this be incorporated into foundation?

https://github.com/nh2/haskell-ordnub

[vincenthz]

definitely, related to #135

[ndmitchell]

Alternatively you might want to do a hash based nub etc.

[flip111]

Seems to be a duplicate of #135

[flip111]

Actually #135 is only about nub .. so I reopen it for the other functions