fix ByteString conversion on windows

the encode' and decode' functions on Windows should not apply the
filesystem encoding, which does not work there. Instead, convert to and
from UTF-8.

Also, avoid exporting encodeW8 and decodeW8. Both use the filesystem
encoding, so won't work as expected on windows.

Utility/Metered.hs

@@ -258,7 +258,7 @@ commandMeter' progressparser oh meterupdate cmd params =
 				unless (quietMode oh) $ do
 					S.hPut stdout b
 					hFlush stdout
-				let s = encodeW8 (S.unpack b)
+				let s = decodeBS b
 				let (mbytes, buf') = progressparser (buf++s)
 				case mbytes of
 					Nothing -> feedprogress prev buf' h