Add php_serialize session.serialize_handler. This patch closes

  Request #25630
  Request #43980
  Request #54383
  Bug #65359

and many others similar to these that are closed as "wont fix" or
"not a bug".

Current serializers have limitations due to register_globals support
that are no longer supported. Changing existing serializer may cause
compatibility issue. Therefore, new handler is needed to remove
needless limitations.

php_serialize does not have special characters and allow numerical
index in $_SESSION. $_SESSION can be used as ordinary array.