Make aapt warning concise

The previous warning made it seem like it could be using the value
specified on the command line, but, in fact, it would ignore the command
line value if it were already specified in the AndroidManifest.xml

Change-Id: I15e8161e094f17412680d25d3b7b810474eb4a31
diff --git a/tools/aapt/Resource.cpp b/tools/aapt/Resource.cpp
index 87f2420..a8ac2ec 100644
--- a/tools/aapt/Resource.cpp
+++ b/tools/aapt/Resource.cpp
@@ -611,7 +611,8 @@
     const String16 attr(attr8);
     
     if (node->getAttribute(ns, attr) != NULL) {
-        fprintf(stderr, "Warning: AndroidManifest.xml already defines %s (in %s)\n",
+        fprintf(stderr, "Warning: AndroidManifest.xml already defines %s (in %s);"
+                        " using existing value in manifest.\n",
                 String8(attr).string(), String8(ns).string());
         return;
     }