Return an error if default() is used on a local variable.
  This is actaully a side-effect of BUG#5967: Stored procedure declared
  variable used instead of column (to be fixed later), so this is really a
  workaround until that is fixed.


mysql-test/r/sp-error.result:
  New test case for BUG#10969.
mysql-test/t/sp-error.test:
  New test case for BUG#10969.
sql/item.h:
  Get name of local variable for error messages.
sql/sql_yacc.yy:
  Return an error if default() is applied on a local SP variable.