Revert clever target filepath construction.

  * Scripts break with -XOverloadedStrings enabled.

  The problem is simple string literals are used in place of target
  filepaths and that's as intended. But there is no way ghc can figure
  out these string literals should be strings from `Target p => p`
  constraint

  * We want -XOverloadedStrings

  `sudo`, for example, can use overloaded string/number literals to
  provide nice "dslish" way to define the user under which commands should
  be executed

This takes us back to square one: target paths ending in "/" are treated
as directories to place stuff into.