[MARTIFACT-31] ignore remote buildinfo for compare

it may have been generated with other plugin version, then would require
much harder comparison algorithm
diff --git a/src/main/java/org/apache/maven/plugins/artifact/buildinfo/ReferenceBuildinfoUtil.java b/src/main/java/org/apache/maven/plugins/artifact/buildinfo/ReferenceBuildinfoUtil.java
index 1203922..00516af 100644
--- a/src/main/java/org/apache/maven/plugins/artifact/buildinfo/ReferenceBuildinfoUtil.java
+++ b/src/main/java/org/apache/maven/plugins/artifact/buildinfo/ReferenceBuildinfoUtil.java
@@ -56,7 +56,7 @@
 import java.util.zip.ZipEntry;
 
 /**
- * Utility to download or generate reference buildinfo.
+ * Utility to download reference artifacts and download or generate reference buildinfo.
  */
 class ReferenceBuildinfoUtil
 {
@@ -111,6 +111,14 @@
     {
         File referenceBuildinfo = downloadReferenceBuildinfo( repo, project );
 
+        if ( referenceBuildinfo != null )
+        {
+            log.warn( "dropping downloaded reference buildinfo because it may be generated"
+                + " from different maven-artifact-plugin release..." );
+            // TODO keep a save?
+            referenceBuildinfo = null;
+        }
+
         if ( referenceBuildinfo == null )
         {
             // download reference artifacts and guess Java version and OS