use a batch file to run msysgit's ssh, instead of copying

copying failed because dlls are not in path.

This batch file is based on the one msysgit uses to start gitk

Build/NullSoftInstaller.hs

@@ -54,7 +54,7 @@ main = do
 		let htmlhelp = tmpdir </> "git-annex.html"
 		writeFile htmlhelp htmlHelpText
 		writeFile nsifile $ makeInstaller gitannex license htmlhelp
-			(catMaybes (extrabins ++ dllpaths))
+			(wrappers ++ catMaybes (extrabins ++ dllpaths))
 			[ webappscript, autostartscript ]
 		mustSucceed "makensis" [File nsifile]
 	removeFile nsifile -- left behind if makensis fails
@@ -152,9 +152,6 @@ makeInstaller gitannex license htmlhelp extrabins launchers = nsis $ do
 	section "cmd" [] $ do
 		setOutPath "$INSTDIR\\cmd"
 		mapM_ addfile (gitannex:extrabins)
-		-- copy msysgit's ssh into cmd so it's always in PATH
-		-- (bin is only in PATH from git bash)
-		copyFiles [] "$INSTDIR\\bin\\ssh.exe" "$INSTDIR\\cmd\\ssh.exe"
 	section "meta" [] $ do
 		setOutPath "$INSTDIR\\doc\\git\\html"
 		addfile htmlhelp
@@ -200,3 +197,6 @@ findCygLibs p = filter iscyg . mapMaybe parse . lines <$> readProcess "ldd" [p]
 		(dll:"=>":_dllpath:_offset:[]) -> Just dll
 		_ -> Nothing
 	iscyg f = "cyg" `isPrefixOf` f || "lib" `isPrefixOf` f
+
+wrappers :: [FilePath]
+wrappers = ["standalone\\windows\\ssh.cmd"]