correct value of CURRENT_USER() in SP with "security definer" (BUG#7291)


BitKeeper/etc/config:
  switch off open logging
mysql-test/r/sp-security.result:
  correct value from current_user() in function run from "security definer"
mysql-test/r/view.result:
  evaluation constant functions in WHERE (BUG#4663)
mysql-test/t/sp-security.test:
  correct value from current_user() in function run from "security definer"
mysql-test/t/view.test:
  evaluation constant functions in WHERE (BUG#4663)
sql/item.cc:
  Item_static_string_func creation if it is need
sql/item.h:
  support of Item_static_string_func creation
sql/item_cmpfunc.cc:
  do not evaluate items during view creation
sql/item_create.cc:
  create Item_func_user
sql/item_strfunc.cc:
  Item_func_sysconst in case of converting value still have to correctly print itself
  => use Item_static_string_func instead of Item_string
      Item_func_user return USER() or CURRENT_USER()
sql/item_strfunc.h:
  support of correct charset conversion procedure in Item_func_sysconst
sql/sql_class.h:
  new method
sql/sql_yacc.yy:
  Item_func_user now support both USER() and CURRENT_USER(), so we have to pass parametr what it is