Shadowed dependencies with custom Setup.hs

[quasicomputational]

I am afraid I don't have a small reproducer for this and it doesn't happen on my machine, but have a look at this Travis build log that failed. #3503 fixed this problem elsewhere, but maybe it was incomplete for custom Setup.hs components?

[quasicomputational]

FWIW this stopped happening when I disabled caching of $HOME/.stack, and seems to have stopped for good now that I've removed transformers-0.5.5.0 from the extra-deps and re-enabled caching.