delete is declared. As we don't use exceptions placement delete is never 
called and the fix only affects numerous warnings when
compiling with MS Visual C++.
For more info see http://www.gotw.ca/gotw/010.htm.


sql/item.h:
  Fix the signature of placement operator delete for class Item.
sql/sql_class.cc:
  Add placement delete operator to suppress a warning under Windows.
sql/sql_lex.h:
  Fix the signature of placement operator delete for class LEX
sql/sql_list.h:
  Fix the signature of placement operator delete for class Sql_alloc
sql/sql_string.h:
  Fix the signature of placement operator delete for class Sql_string