Make sure the JobControl module is part of the dist.

cabal-install/cabal-install.cabal

@@ -86,6 +86,7 @@ Executable cabal
         Distribution.Client.Install
         Distribution.Client.InstallPlan
         Distribution.Client.InstallSymlink
+        Distribution.Client.JobControl        
         Distribution.Client.List
         Distribution.Client.PackageIndex
         Distribution.Client.PackageUtils