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)

plugin/auth_examples/qa_auth_interface.c

@@ -68,7 +68,7 @@ static int qa_auth_interface (MYSQL_PLUGIN_VIO *vio, MYSQL_SERVER_AUTH_INFO *inf
   else if (strcmp(info->user_name, "qa_test_2_user")== 0)
   {
     /* Overwriting not intended, but with effect on USER() */
-     strcpy(info->user_name, "user_name");
+    strcpy((char*) info->user_name, "user_name");
      info->user_name_length= 9;
     /* Overwriting not intended, effect not visible */
      strcpy((char *)info->auth_string, "auth_string");
@@ -107,7 +107,7 @@ static int qa_auth_interface (MYSQL_PLUGIN_VIO *vio, MYSQL_SERVER_AUTH_INFO *inf
   else if (strcmp(info->user_name, "qa_test_5_user")== 0)  
   {
 /* This assignment has no effect.*/
-     strcpy(info->user_name, "");
+    strcpy((char*) info->user_name, "");
      info->user_name_length= 0;
 /* This assignment has no effect.*/
      strcpy((char *)info->auth_string, "");

plugin/feedback/feedback.cc

@@ -93,8 +93,8 @@ static COND* make_cond(THD *thd, TABLE_LIST *tables, LEX_STRING *filter)
 {
   Item_cond_or *res= NULL;
   Name_resolution_context nrc;
-  const char *db= tables->db, *table= tables->alias,
-             *field= tables->table->field[0]->field_name;
+  const char *db= tables->db, *table= tables->alias;
+  LEX_CSTRING *field= &tables->table->field[0]->field_name;
   CHARSET_INFO *cs= &my_charset_latin1;
 
   if (!filter->str)

plugin/handler_socket/handlersocket/database.cpp

@@ -1085,8 +1085,8 @@ dbcontext::parse_fields(TABLE *const table, const char *str,
     Field **fld = 0;
     size_t j = 0;
     for (fld = table->field; *fld; ++fld, ++j) {
-      DBG_FLD(fprintf(stderr, "f %s\n", (*fld)->field_name));
-      string_ref fn((*fld)->field_name, strlen((*fld)->field_name));
+      DBG_FLD(fprintf(stderr, "f %s\n", (*fld)->field_name.str));
+      string_ref fn((*fld)->field_name.str, (*fld)->field_name.length);
       if (fn == fldnms[i]) {
 	break;
       }
@@ -1096,7 +1096,7 @@ dbcontext::parse_fields(TABLE *const table, const char *str,
 	std::string(fldnms[i].begin(), fldnms[i].size()).c_str()));
       return false;
     }
-    DBG_FLD(fprintf(stderr, "FLD %s %zu\n", (*fld)->field_name, j));
+    DBG_FLD(fprintf(stderr, "FLD %s %zu\n", (*fld)->field_name.str, j));
     flds.push_back(j);
   }
   return true;

plugin/qc_info/qc_info.cc

@@ -142,7 +142,7 @@ static int qc_info_fill_table(THD *thd, TABLE_LIST *tables,
     size_t flags_length;
     const char *key, *db;
     size_t key_length, db_length;
-    LEX_STRING sql_mode_str;
+    LEX_CSTRING sql_mode_str;
     const String *tz;
     CHARSET_INFO *cs_client;
     CHARSET_INFO *cs_result;

plugin/simple_password_check/simple_password_check.c

@@ -23,7 +23,8 @@
 
 static unsigned min_length, min_digits, min_letters, min_others;
 
-static int validate(MYSQL_LEX_STRING *username, MYSQL_LEX_STRING *password)
+static int validate(MYSQL_CONST_LEX_STRING *username,
+                    MYSQL_CONST_LEX_STRING *password)
 {
   unsigned digits=0 , uppers=0 , lowers=0, others=0, length= password->length;
   const char *ptr= password->str, *end= ptr + length;