Changing field::field_name and Item::name to LEX_CSTRING

Benefits of this patch:
- Removed a lot of calls to strlen(), especially for field_string
- Strings generated by parser are now const strings, less chance of
  accidently changing a string
- Removed a lot of calls with LEX_STRING as parameter (changed to pointer)
- More uniform code
- Item::name_length was not kept up to date. Now fixed
- Several bugs found and fixed (Access to null pointers,
  access of freed memory, wrong arguments to printf like functions)
- Removed a lot of casts from (const char*) to (char*)

Changes:
- This caused some ABI changes
  - lex_string_set now uses LEX_CSTRING
  - Some fucntions are now taking const char* instead of char*
- Create_field::change and after changed to LEX_CSTRING
- handler::connect_string, comment and engine_name() changed to LEX_CSTRING
- Checked printf() related calls to find bugs. Found and fixed several
  errors in old code.
- A lot of changes from LEX_STRING to LEX_CSTRING, especially related to
  parsing and events.
- Some changes from LEX_STRING and LEX_STRING & to LEX_CSTRING*
- Some changes for char* to const char*
- Added printf argument checking for my_snprintf()
- Introduced null_clex_str, star_clex_string, temp_lex_str to simplify
  code
- Added item_empty_name and item_used_name to be able to distingush between
  items that was given an empty name and items that was not given a name
  This is used in sql_yacc.yy to know when to give an item a name.
- select table_name."*' is not anymore same as table_name.*
- removed not used function Item::rename()
- Added comparision of item->name_length before some calls to
  my_strcasecmp() to speed up comparison
- Moved Item_sp_variable::make_field() from item.h to item.cc
- Some minimal code changes to avoid copying to const char *
- Fixed wrong error message in wsrep_mysql_parse()
- Fixed wrong code in find_field_in_natural_join() where real_item() was
  set when it shouldn't
- ER_ERROR_ON_RENAME was used with extra arguments.
- Removed some (wrong) ER_OUTOFMEMORY, as alloc_root will already
  give the error.

TODO:
- Check possible unsafe casts in plugin/auth_examples/qa_auth_interface.c
- Change code to not modify LEX_CSTRING for database name
  (as part of lower_case_table_names)

sql/sql_rename.cc

@@ -33,8 +33,8 @@
 
 static TABLE_LIST *rename_tables(THD *thd, TABLE_LIST *table_list,
 				 bool skip_error);
-static bool do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db,
-                      char *new_table_name, char *new_table_alias,
+static bool do_rename(THD *thd, TABLE_LIST *ren_table, const char *new_db,
+                      const char *new_table_name, const char *new_table_alias,
                       bool skip_error);
 
 static TABLE_LIST *reverse_table_list(TABLE_LIST *table_list);
@@ -50,7 +50,7 @@ bool mysql_rename_tables(THD *thd, TABLE_LIST *table_list, bool silent)
   bool binlog_error= 0;
   TABLE_LIST *ren_table= 0;
   int to_table;
-  char *rename_log_table[2]= {NULL, NULL};
+  const char *rename_log_table[2]= {NULL, NULL};
   DBUG_ENTER("mysql_rename_tables");
 
   /*
@@ -254,8 +254,9 @@ do_rename_temporary(THD *thd, TABLE_LIST *ren_table, TABLE_LIST *new_table,
 */
 
 static bool
-do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db, char *new_table_name,
-          char *new_table_alias, bool skip_error)
+do_rename(THD *thd, TABLE_LIST *ren_table, const char *new_db,
+          const char *new_table_name, const char *new_table_alias,
+          bool skip_error)
 {
   int rc= 1;
   handlerton *hton;
@@ -291,11 +292,11 @@ do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db, char *new_table_name,
       if (!(rc= mysql_rename_table(hton, ren_table->db, old_alias,
                                    new_db, new_alias, 0)))
       {
-        LEX_STRING db_name= { ren_table->db, ren_table->db_length };
-        LEX_STRING table_name= { ren_table->table_name,
+        LEX_CSTRING db_name= { ren_table->db, ren_table->db_length };
+        LEX_CSTRING table_name= { ren_table->table_name,
                                  ren_table->table_name_length };
-        LEX_STRING new_table= { (char *) new_alias, strlen(new_alias) };
-        LEX_STRING new_db_name= { (char*)new_db, strlen(new_db)};
+        LEX_CSTRING new_table= { new_alias, strlen(new_alias) };
+        LEX_CSTRING new_db_name= { new_db, strlen(new_db)};
         (void) rename_table_in_stat_tables(thd, &db_name, &table_name,
                                            &new_db_name, &new_table);
         if ((rc= Table_triggers_list::change_table_name(thd, ren_table->db,