Prohibit duplicate addition of aspect to an attribute and improve diagnostics.

--
MOS_MIGRATED_REVID=127808009
diff --git a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
index 848cdcc..7256393 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/SkylarkAttr.java
@@ -1247,7 +1247,7 @@
           throw new EvalException(definitionLocation,
               "All aspects applied to rule dependencies must be top-level values");
         }
-        attributeBuilder.aspect(skylarkAspect);
+        attributeBuilder.aspect(skylarkAspect, definitionLocation);
       }
       exported = true;
     }