make opening file browser work on windows

Assistant/WebApp/DashBoard.hs

@@ -118,21 +118,27 @@ getFileBrowserR = whenM openFileBrowser redirectBack
 openFileBrowser :: Handler Bool
 openFileBrowser = do
 	path <- liftAnnex $ fromRepo Git.repoPath
-	ifM (liftIO $ inPath cmd <&&> inPath cmd)
+#ifdef darwin_HOST_OS
+	let cmd = "open"
+	let params = [Param path]
+#else
+#ifdef mingw32_HOST_OS
+	let cmd = "cmd"
+	let params = [Param $ "/c start " ++ path]
+#else
+	let cmd = "xdg-open"
+	let params = [Param path]
+#endif
+#endif
+	ifM (liftIO $ inPath cmd)
 		( do
 			void $ liftIO $ forkIO $ void $
-				boolSystem cmd [Param path]
+				boolSystem cmd params
 			return True
 		, do
 			void $ redirect $ "file://" ++ path
 			return False
 		)
-  where
-#ifdef darwin_HOST_OS
-	cmd = "open"
-#else
-	cmd = "xdg-open"
-#endif
 
 {- Transfer controls. The GET is done in noscript mode and redirects back
  - to the referring page. The POST is called by javascript. -}