BUG#12427262 : 60961: SHOW TABLES VERY SLOW WHEN NOT IN SYSTEM DISK CACHE

Reason:
 This is a regression happened because of changes done in code refactoring 
 in 5.1 from 5.0.

Issue: 
 While doing "Show tables" lex->verbose was being checked to avoid opening
 FRM files to get table type. In case of "Show full table", lex->verbose
 is true to indicate table type is required. In 5.0, this check was
 present which got missing in >=5.5.

Fix:
 Added the required check to avoid opening FRM files unnecessarily in case
 of "Show tables".

sql/sql_show.cc

@@ -3198,8 +3198,12 @@ end:
 
 static int fill_schema_table_names(THD *thd, TABLE *table,
                                    LEX_STRING *db_name, LEX_STRING *table_name,
-                                   bool with_i_schema)
+                                   bool with_i_schema,
+                                   bool need_table_type)
 {
+  /* Avoid opening FRM files if table type is not needed. */
+  if (need_table_type)
+  {
     if (with_i_schema)
     {
       table->field[3]->store(STRING_WITH_LEN("SYSTEM VIEW"),
@@ -3233,6 +3237,7 @@ static int fill_schema_table_names(THD *thd, TABLE *table,
         return 0;
       }
     }
+  }
   if (schema_table_store_record(thd, table))
     return 1;
   return 0;
@@ -3551,7 +3556,8 @@ int get_all_tables(THD *thd, TABLE_LIST *tables, COND *cond)
           if (schema_table_idx == SCH_TABLE_NAMES)
           {
             if (fill_schema_table_names(thd, tables->table, db_name,
-                                        table_name, with_i_schema))
+                                        table_name, with_i_schema,
+                                        lex->verbose))
               continue;
           }
           else