Fix failed assertion in 'InstallPlan.processing'.

Triggered by 'linearizeInstallPlan'. Fixes #1619.

cabal-install/Distribution/Client/Install.hs

@@ -505,7 +505,8 @@ linearizeInstallPlan installedPkgIndex plan =
           status = packageStatus installedPkgIndex pkg
           plan'' = InstallPlan.completed pkgid
                      (BuildOk DocsNotTried TestsNotTried
-                              (Just Installed.emptyInstalledPackageInfo))
+                              (Just $ Installed.emptyInstalledPackageInfo
+                              { Installed.sourcePackageId = pkgid }))
                      (InstallPlan.processing [pkg] plan')
           --FIXME: This is a bit of a hack,
           -- pretending that each package is installed

cabal-install/Distribution/Client/InstallPlan.hs

@@ -349,7 +349,7 @@ showPlanProblem (PackageInvalid pkg packageProblems) =
 
 showPlanProblem (PackageMissingDeps pkg missingDeps) =
      "Package " ++ display (packageId pkg)
-  ++ " depends on the following packages which are missing from the plan "
+  ++ " depends on the following packages which are missing from the plan: "
   ++ intercalate ", " (map display missingDeps)
 
 showPlanProblem (PackageCycle cycleGroup) =