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)

include/m_string.h

@@ -212,11 +212,6 @@ extern ulonglong strtoull(const char *str, char **ptr, int base);
 #define USTRING_WITH_LEN(X) ((uchar*) X), ((size_t) (sizeof(X) - 1))
 #define C_STRING_WITH_LEN(X) ((char *) (X)), ((size_t) (sizeof(X) - 1))
 
-struct st_mysql_const_lex_string
-{
-  const char *str;
-  size_t length;
-};
 typedef struct st_mysql_const_lex_string LEX_CSTRING;
 
 /* A variant with const and unsigned */
@@ -227,15 +222,15 @@ struct st_mysql_const_unsigned_lex_string
 };
 typedef struct st_mysql_const_unsigned_lex_string LEX_CUSTRING;
 
-static inline void lex_string_set(LEX_STRING *lex_str, const char *c_str)
+static inline void lex_string_set(LEX_CSTRING *lex_str, const char *c_str)
 {
-  lex_str->str= (char *) c_str;
+  lex_str->str= c_str;
   lex_str->length= strlen(c_str);
 }
-static inline void lex_string_set3(LEX_STRING *lex_str, const char *c_str,
+static inline void lex_string_set3(LEX_CSTRING *lex_str, const char *c_str,
                                    size_t len)
 {
-  lex_str->str= (char *) c_str;
+  lex_str->str= c_str;
   lex_str->length= len;
 }