typo fixed

mysql-test/r/mysqld--help.result

@@ -1024,7 +1024,7 @@ The following options may be given as the first argument:
  (usually get from GUI tools)
  --use-stat-tables=name 
  Specifies how to use system statistics tables. Possible
- values are NEVER, COMPLEMENTARY, PREVERABLY
+ values are NEVER, COMPLEMENTARY, PREFERABLY
  -u, --user=name     Run mysqld daemon as user.
  --userstat          Enables statistics gathering for USER_STATISTICS,
  CLIENT_STATISTICS, INDEX_STATISTICS and TABLE_STATISTICS

sql/sys_vars.cc

@@ -4586,7 +4586,7 @@ const char *use_stat_tables_modes[] =
 static Sys_var_enum Sys_optimizer_use_stat_tables(
        "use_stat_tables",
        "Specifies how to use system statistics tables. Possible values are "
-       "NEVER, COMPLEMENTARY, PREVERABLY",
+       "NEVER, COMPLEMENTARY, PREFERABLY",
        SESSION_VAR(use_stat_tables), CMD_LINE(REQUIRED_ARG),
        use_stat_tables_modes, DEFAULT(0));