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_admin.cc

@@ -189,7 +189,7 @@ static int prepare_for_repair(THD *thd, TABLE_LIST *table_list,
   if (!mysql_file_stat(key_file_misc, from, &stat_info, MYF(0)))
     goto end;				// Can't use USE_FRM flag
 
-  my_snprintf(tmp, sizeof(tmp), "%s-%lx_%lx",
+  my_snprintf(tmp, sizeof(tmp), "%s-%lx_%llx",
 	      from, current_pid, thd->thread_id);
 
   if (table_list->table)
@@ -489,7 +489,7 @@ static bool mysql_admin_table(THD* thd, TABLE_LIST* tables,
   for (table= tables; table; table= table->next_local)
   {
     char table_name[SAFE_NAME_LEN*2+2];
-    char* db = table->db;
+    const char *db= table->db;
     bool fatal_error=0;
     bool open_error;
     bool collect_eis=  FALSE;
@@ -842,7 +842,7 @@ static bool mysql_admin_table(THD* thd, TABLE_LIST* tables,
               push_warning_printf(thd, Sql_condition::WARN_LEVEL_WARN,
                                   ER_NO_EIS_FOR_FIELD,
                                   ER_THD(thd, ER_NO_EIS_FOR_FIELD),
-                                  (*field_ptr)->field_name);
+                                  (*field_ptr)->field_name.str);
           }
         }
         else
@@ -1234,7 +1234,7 @@ err2:
 */
 
 bool mysql_assign_to_keycache(THD* thd, TABLE_LIST* tables,
-			     LEX_STRING *key_cache_name)
+			     const LEX_CSTRING *key_cache_name)
 {
   HA_CHECK_OPT check_opt;
   KEY_CACHE *key_cache;