add png to makefile for linux



git-svn-id: http://skia.googlecode.com/svn/trunk@551 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tools/skhello.cpp b/tools/skhello.cpp
index 6f56d4c..179c3da 100644
--- a/tools/skhello.cpp
+++ b/tools/skhello.cpp
@@ -57,9 +57,11 @@
                     SkIntToScalar(w)/2, SkIntToScalar(h)*2/3,
                     paint);
 
-    SkImageEncoder::EncodeFile(path.c_str(), bitmap,
+    bool success = SkImageEncoder::EncodeFile(path.c_str(), bitmap,
                                SkImageEncoder::kPNG_Type, 100);
-
-    return 0;
+    if (!success) {
+        SkDebugf("--- failed to write %s\n", path.c_str());
+    }
+    return !success;
 }