Use haskell setenv library to clean up several ugly workarounds for inability to manipulate the environment on windows.

Didn't know that this library existed!

This includes making git-annex not re-exec itself on start on windows, and
making the test suite on Windows run tests without forking.

Utility/Lsof.hs

@@ -32,7 +32,7 @@ setup = do
 	when (isAbsolute cmd) $ do
 		path <- getSearchPath
 		let path' = takeDirectory cmd : path
-		void $ setEnv "PATH" (intercalate [searchPathSeparator] path') True
+		setEnv "PATH" (intercalate [searchPathSeparator] path') True
 
 {- Checks each of the files in a directory to find open files.
  - Note that this will find hard links to files elsewhere that are open. -}