upload: fix URI bug and always use new hackage URI

Previously, when uriPath was "", then the generated URI would be wrong. For example,
if we have a remote repo with the URI http://hackage.haskell.org (without a trailing slash),
then the previous code will generate http://hackage.haskell.orgupload for the upload URL.
We now use the relativeTo function from Network.URI, which does the right thing.

Additionaly, we now always rely on the new hackage URL layout. cabal now automatically
upgrades the old URI to the new URI when parsing the config file, so manually checking
for that is no longer needed.

cabal-install/Distribution/Client/Upload.hs

@@ -5,7 +5,7 @@ module Distribution.Client.Upload (check, upload, report) where
 
 import Distribution.Client.Types (Username(..), Password(..),Repo(..),RemoteRepo(..))
 import Distribution.Client.HttpUtils
-         ( isOldHackageURI, HttpTransport(..), remoteRepoTryUpgradeToHttps )
+         ( HttpTransport(..), remoteRepoTryUpgradeToHttps )
 
 import Distribution.Simple.Utils (notice, warn, info, die)
 import Distribution.Verbosity (Verbosity)
@@ -15,7 +15,7 @@ import Distribution.Client.Config
 import qualified Distribution.Client.BuildReports.Anonymous as BuildReport
 import qualified Distribution.Client.BuildReports.Upload as BuildReport
 
-import Network.URI (URI(uriPath), parseURI)
+import Network.URI (URI(uriPath), parseURI, parseRelativeReference, relativeTo)
 
 import System.IO        (hFlush, stdin, stdout, hGetEcho, hSetEcho)
 import Control.Exception (bracket)
@@ -26,10 +26,8 @@ import Control.Monad (forM_, when)
 
 type Auth = Maybe (String, String)
 
---FIXME: how do we find this path for an arbitrary hackage server?
--- is it always at some fixed location relative to the server root?
-legacyUploadURI :: URI
-Just legacyUploadURI = parseURI "http://hackage.haskell.org/cgi-bin/hackage-scripts/protected/upload-pkg"
+uploadReference :: URI
+Just uploadReference = parseRelativeReference "/upload"
 
 checkURI :: URI
 Just checkURI = parseURI "http://hackage.haskell.org/cgi-bin/hackage-scripts/check-pkg"
@@ -41,13 +39,7 @@ upload transport verbosity repos mUsername mPassword paths = do
         [] -> die $ "Cannot upload. No remote repositories are configured."
         rs -> remoteRepoTryUpgradeToHttps transport (last rs)
     let targetRepoURI = remoteRepoURI targetRepo
-        uploadURI
-          | isOldHackageURI targetRepoURI
-          = legacyUploadURI
-          | otherwise
-          = targetRepoURI {
-              uriPath = uriPath targetRepoURI FilePath.Posix.</> "upload"
-            }
+        uploadURI = uploadReference `relativeTo` targetRepoURI
     Username username <- maybe promptUsername return mUsername
     Password password <- maybe promptPassword return mPassword
     let auth = Just (username,password)