renumber diagnostic to avoid conflict

specialization nabbed E0520

src/librustc_metadata/creader.rs

@@ -298,7 +298,7 @@ impl<'a> CrateReader<'a> {
             if other.name() == crate_name && // same crate-name
                other.disambiguator() == disambiguator &&  // same crate-disambiguator
                other.hash() != svh { // but different SVH
-                span_fatal!(self.sess, span, E0520,
+                span_fatal!(self.sess, span, E0521,
                         "found two different crates with name `{}` that are \
                          not distinguished by differing `-C metadata`. This \
                          will result in symbol conflicts between the two.",

src/librustc_metadata/diagnostics.rs

@@ -88,5 +88,5 @@ register_diagnostics! {
     E0469, // imported macro not found
     E0470, // reexported macro not found
     E0519, // local crate and dependency have same (crate-name, disambiguator)
-    E0520, // two dependencies have same (crate-name, disambiguator) but different SVH
+    E0521, // two dependencies have same (crate-name, disambiguator) but different SVH
 }