Fix 'n' concurrent prepared executions

sql/sql_prepare.cc:
  Fix 'n' concurrent executions
libmysql/errmsg.c:
  Fix the missing semicolon for errors
libmysql/libmysql.c:
  Fix the result meta info for non-SELECT statements

sql/sql_class.h

@@ -327,6 +327,7 @@ public:
 typedef struct st_prep_stmt
 {
   THD *thd;
+  LEX  lex; 
   Item_param **param;
   Item *free_list;
   MEM_ROOT mem_root;