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_sequence.cc

@@ -28,7 +28,7 @@ struct Field_definition
   const char *field_name;
   uint length;
   enum enum_field_types sql_type;
-  LEX_STRING comment;
+  LEX_CSTRING comment;
   ulong flags;
 };
 
@@ -45,19 +45,19 @@ struct Field_definition
 
 static Field_definition sequence_structure[]=
 {
-  {"next_value", 21, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("next not cached value")},
+  {"next_value", 21, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("next not cached value")},
    FL},
-  {"min_value", 21, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("min value")}, FL},
-  {"max_value", 21, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("max value")}, FL},
-  {"start", 21, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("start value")},  FL},
+  {"min_value", 21, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("min value")}, FL},
+  {"max_value", 21, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("max value")}, FL},
+  {"start", 21, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("start value")},  FL},
   {"increment", 21, MYSQL_TYPE_LONGLONG,
    {C_STRING_WITH_LEN("increment value")}, FL},
-  {"cache", 21, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("cache size")}, FL},
-  {"cycle", 1, MYSQL_TYPE_TINY, {C_STRING_WITH_LEN("cycle state")},
+  {"cache", 21, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("cache size")}, FL},
+  {"cycle", 1, MYSQL_TYPE_TINY, {STRING_WITH_LEN("cycle state")},
    FL | UNSIGNED_FLAG },
   {"round", 21, MYSQL_TYPE_LONGLONG,
-   {C_STRING_WITH_LEN("How many cycles has been done")}, FL},
-  {NULL, 0, MYSQL_TYPE_LONGLONG, {C_STRING_WITH_LEN("")}, 0}
+   {STRING_WITH_LEN("How many cycles has been done")}, FL},
+  {NULL, 0, MYSQL_TYPE_LONGLONG, {STRING_WITH_LEN("")}, 0}
 };
 
 #undef FL
@@ -194,11 +194,11 @@ bool check_sequence_fields(LEX *lex, List<Create_field> *fields)
   {
     Field_definition *field_def= &sequence_structure[field_no];
     if (my_strcasecmp(system_charset_info, field_def->field_name,
-                      field->field_name) ||
+                      field->field_name.str) ||
         field->flags != field_def->flags ||
         field->sql_type != field_def->sql_type)
     {
-      reason= field->field_name;
+      reason= field->field_name.str;
       goto err;
     }
   }
@@ -228,10 +228,13 @@ bool prepare_sequence_fields(THD *thd, List<Create_field> *fields)
   for (field_info= sequence_structure; field_info->field_name ; field_info++)
   {
     Create_field *new_field;
+    LEX_CSTRING field_name= {field_info->field_name,
+                             strlen(field_info->field_name)};
+
     if (unlikely(!(new_field= new Create_field())))
       DBUG_RETURN(TRUE); /* purify inspected */
 
-    new_field->field_name=  field_info->field_name;
+    new_field->field_name=  field_name;
     new_field->sql_type=    field_info->sql_type;
     new_field->length=      field_info->length;
     new_field->char_length= field_info->length;