* Simplify @-patterns: only {attrs}@name' or name@{attrs}' are now

allowed.  So `name1@name2', `{attrs1}@{attrs2}' and so on are now no
  longer legal.  This is no big loss because they were not useful
  anyway.

  This also changes the output of builtins.toXML for @-patterns
  slightly.

src/libexpr/primops.cc

@@ -846,19 +846,14 @@ static void attrsInPattern(ATermMap & map, Pattern pat)
 {
     ATerm name;
     ATermList formals;
-    Pattern pat1, pat2;
     ATermBool ellipsis;
-    if (matchAttrsPat(pat, formals, ellipsis)) { 
+    if (matchAttrsPat(pat, formals, ellipsis, name)) { 
         for (ATermIterator i(formals); i; ++i) {
             ATerm def;
             if (!matchFormal(*i, name, def)) abort();
             map.set(name, makeAttrRHS(makeBool(def != constNoDefaultValue), makeNoPos()));
         }
     }
-    else if (matchAtPat(pat, pat1, pat2)) {
-        attrsInPattern(map, pat1);
-        attrsInPattern(map, pat2);
-    }
 }