rare spec dupe check

server/src/cryp.rs

@@ -295,7 +295,10 @@ impl Cryp {
                     return Err(format_err!("cryp at maximum rare specalisations ({:})", max_rare))
                 }
 
-                // check dupes
+                if self.specs.rare.iter().find(|s| s.spec == spec.spec).is_some() {
+                    return Err(format_err!("duplicate rare specialisation {:?}", spec.spec));
+                }
+
                 self.specs.rare.push(spec);
             },
         };