Allow LinkGenerator to be overridden by autoconfiguration

Author: jdaugherty

grails-plugin-url-mappings/src/main/groovy/org/grails/plugins/web/mapping/UrlMappingsAutoConfiguration.java

@@ -47,6 +47,7 @@ public UrlConverter hyphenatedUrlConverter() {
     }
 
     @Bean
+    @ConditionalOnMissingBean(name = LinkGenerator.BEAN_NAME)
     public LinkGenerator grailsLinkGenerator() {
         if (cacheUrls == null) {
             cacheUrls = !Environment.isDevelopmentMode() && !Environment.getCurrent().isReloadEnabled();

grails-web-url-mappings/src/main/groovy/grails/web/mapping/LinkGenerator.java

@@ -28,6 +28,7 @@
  */
 public interface LinkGenerator {
 
+    String BEAN_NAME = "grailsLinkGenerator";
     String ATTRIBUTE_CONTROLLER = "controller";
     String ATTRIBUTE_RESOURCE = "resource";
     String ATTRIBUTE_ACTION = "action";