Executable built with cabal-dev is not subsequently used by cabal-dev

[atzedijkstra]

When building wxHaskell (after checking out the wx sources) with cabal-dev by:

cabal-dev install ./wxdirect ./wxc ./wxcore ./wx

the built wxdirect is not subsequently used, but instead the global one is used, even after hiding the globally installed one and moving its executable. It is (of course) possible to work around it by globally changing the shell search path, but this is not a flexible sandboxing solution.