Avoid creating a new String to qualify types

- This is now slightly faster, which for a method that gets called
    over 1 million times on large projects is significant.
 - We should still look for ways to reduce the number of calls to this
    method.

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/symboltable/ClassScope.java

@@ -341,7 +341,7 @@ public class ClassScope extends AbstractJavaScope {
         for (String qualified : qualifiedNames) {
             int fullLength = qualified.length();
             if (qualified.endsWith(typeImage)
-                    && (fullLength == nameLength || qualified.substring(0, fullLength - nameLength).endsWith("."))) {
+                    && (fullLength == nameLength || qualified.charAt(fullLength - nameLength - 1) == '.')) {
                 return qualified;
             }
         }