Fix error detection for a non-existent global script.

lib/src/global_packages.dart

Index: lib/src/global_packages.dart
diff --git a/lib/src/global_packages.dart b/lib/src/global_packages.dart
index c58ed54c63749028f79ee2b2a24d59a97e9ae064..d3f0112b30896cb19b1c20a739bcc90fbdbe1ae6 100644
--- a/lib/src/global_packages.dart
+++ b/lib/src/global_packages.dart
@@ -123,7 +123,7 @@ class GlobalPackages {
   /// Otherwise, the previous ones will be preserved.
   Future activatePath(String path, List<String> executables,
       {bool overwriteBinStubs}) async {
-    var entrypoint = new Entrypoint(path, cache);
+    var entrypoint = new Entrypoint(path, cache, isGlobal: true);
 
     // Get the package's dependencies.
     await entrypoint.acquireDependencies(SolveType.GET);
@@ -172,7 +172,8 @@ class GlobalPackages {
 
     // Load the package graph from [result] so we don't need to re-parse all
     // the pubspecs.
-    var entrypoint = new Entrypoint.fromSolveResult(root, cache, result);
+    var entrypoint = new Entrypoint.fromSolveResult(root, cache, result,
+        isGlobal: true);
     var snapshots = await _precompileExecutables(entrypoint, dep.name);
     _writeLockFile(dep.name, lockFile);
     writeTextFile(_getPackagesFilePath(dep.name), lockFile.packagesFile());
@@ -312,14 +313,14 @@ class GlobalPackages {
       // lockfile is the one we just loaded.
       var dir = cache.sources[id.source].getDirectory(id);
       var package = new Package.load(name, dir, cache.sources);
-      return new Entrypoint.inMemory(package, lockFile, cache);
+      return new Entrypoint.inMemory(package, lockFile, cache, isGlobal: true);
     }
 
     // For uncached sources (i.e. path), the ID just points to the real
     // directory for the package.
     assert(id.source == "path");
-    return new Entrypoint(PathSource.pathFromDescription(id.description),
-        cache);
+    return new Entrypoint(
+        PathSource.pathFromDescription(id.description), cache, isGlobal: true);
   }
 
   /// Runs [package]'s [executable] with [args].