Don't change extension of files found in PATH.
Don't change extension of files found in PATH.

See #194.

sdiehl/ghc,sdiehl/ghc,bgamari/shaking-up-ghc,sdiehl/ghc,snowleopard/hadrian,sdiehl/ghc,izgzhen/hadrian,sdiehl/ghc,snowleopard/shaking-up-ghc,sdiehl/ghc,sdiehl/ghc