change to have_<> variable for federated engine

sql/set_var.cc:
  changed 'have_federated_db' to 'have_federated_engine' for consitency, per Paul Dubois

sql/set_var.cc

@@ -732,7 +732,7 @@ struct show_var_st init_vars[]= {
   {"have_crypt",	      (char*) &have_crypt,		    SHOW_HAVE},
   {"have_csv",	              (char*) &have_csv_db,	            SHOW_HAVE},
   {"have_example_engine",     (char*) &have_example_db,	            SHOW_HAVE},
-  {"have_federated_db",       (char*) &have_federated_db,           SHOW_HAVE},
+  {"have_federated_engine",   (char*) &have_federated_db,           SHOW_HAVE},
   {"have_geometry",           (char*) &have_geometry,               SHOW_HAVE},
   {"have_innodb",	      (char*) &have_innodb,		    SHOW_HAVE},
   {"have_isam",		      (char*) &have_isam,		    SHOW_HAVE},