Handle http errors trying to find package (#1552)

lib/src/source/hosted.dart

@@ -315,9 +315,17 @@ class BoundHostedSource extends CachedSource {
   /// Always throws an error, either the original one or a better one.
   void _throwFriendlyError(
       error, StackTrace stackTrace, String package, String url) {
-    if (error is PubHttpException && error.response.statusCode == 404) {
-      throw new PackageNotFoundException(
-          "Could not find package $package at $url.", error, stackTrace);
+    if (error is PubHttpException) {
+      if (error.response.statusCode == 404) {
+        throw new PackageNotFoundException(
+            "Could not find package $package at $url.", error, stackTrace);
+      }
+
+      fail(
+          "${error.response.statusCode} ${error.response.reasonPhrase} trying "
+          "to find package $package at $url.",
+          error,
+          stackTrace);
     }
 
     if (error is io.SocketException) {