deal with Cygwin rsync paths issue

Utility/Path.hs

@@ -17,6 +17,11 @@ import Data.List
 import Data.Maybe
 import Control.Applicative
 
+#ifdef __WINDOWS__
+import Data.Char
+import System.FilePath.Posix as Posix
+#endif
+
 import Utility.Monad
 import Utility.UserInfo
 
@@ -185,3 +190,22 @@ dotfile file
 	| otherwise = "." `isPrefixOf` f || dotfile (takeDirectory file)
   where
 	f = takeFileName file
+
+{- Converts a DOS style path to a Cygwin style path. Only on Windows.
+ - Any trailing '\' is preserved as a trailing '/' -}
+toCygPath :: FilePath -> FilePath
+#ifndef __WINDOWS__
+toCygPath = id
+#else
+toCygPath p
+	| null drive = recombine parts
+	| otherwise = recombine $ "/cygdrive" : driveletter drive : parts
+  where
+  	(drive, p') = splitDrive p
+	parts = splitDirectories p'
+  	driveletter = map toLower . takeWhile (/= ':')
+	recombine = fixtrailing . Posix.joinPath
+  	fixtrailing s
+		| hasTrailingPathSeparator p = Posix.addTrailingPathSeparator s
+		| otherwise = s
+#endif