Require a name for Index annotations because managing indices without a name is

a pain in the ass that we don't particularly need to spend time on.

src/java/com/samskivert/jdbc/depot/annotation/Index.java

@@ -33,7 +33,7 @@ import java.lang.annotation.Target;
 public @interface Index
 {
     /** Defines the name of the index. */
-    String name () default "";
+    String name ();
 
     /** Configures the type of this index if necessary. MySQL supports FULLTEXT, SPATIAL and
      * UNIQUE. */