reproducer for test suite blowup to hand off to ghc folk

I was talking with @AndreasPK , and a more polite version of the blowup that we fixed recently that can easily be built / profiled with ghc master and has < 3gb memusage would be ideal.

@lehins any thoughts on this? (would a version of Test.Vector.Unboxed module work?)

the pre split into modules blowup had the bizzare extreme ~ 16-17gb ram usage, though ghc would only report using ~ 3-6gb?

current theory: O1/O2 have some space leaks that this code exercises.