SEC-799: Add better detection of missing server-ref element for <ldap-user-service> and <ldap-authentication-provider />

http://jira.springframework.org/browse/SEC-799. Updated ContextSourceSettingPostProcessor to set the standard ContextSource as an alias if it is needed by a bean but has not been set (because the user specified their own server id on <ldap-server />).

core/src/test/java/org/springframework/security/config/LdapProviderBeanDefinitionParserTests.java

@@ -75,6 +75,12 @@ public class LdapProviderBeanDefinitionParserTests {
         LdapAuthenticationProvider provider = getProvider();
         provider.authenticate(new UsernamePasswordAuthenticationToken("ben", "ben"));        
     }    
+
+    @Test
+    public void detectsNonStandardServerId() {
+        setContext("<ldap-server id='myServer'/> " +
+                "<ldap-authentication-provider />");
+    }
     
     private void setContext(String context) {
         appCtx = new InMemoryXmlApplicationContext(context);