major refactor of the purging process

src/main/java/fr/xephi/authme/datasource/CacheDataSource.java

@@ -148,6 +148,18 @@ public class CacheDataSource implements DataSource {
         return cleared;
     }
 
+    @Override
+    public Set<String> getRecordsToPurge(long until) {
+        return source.getRecordsToPurge(until);
+    }
+
+    @Override
+    public void purgeRecords(Set<String> toPurge) {
+        for (String name : toPurge) {
+            cachedAuths.invalidate(name);
+        }
+    }
+
     @Override
     public boolean removeAuth(String name) {
         name = name.toLowerCase();