throw an error if response is larger than a limit of 10MB for libxml 2.7.9+

[igorveremsky]

As Alwin commented at http://php.net/manual/en/function.xmlrpc-decode.php:

there is a limit of 10M for response it it exceeded xmlrpc_decode() will return NULL and most of programmers will not know what they do wrong, i spend all day for understand it :) So, i think it can be loged or cathed by this extension and throw an error that max size of response exceeded.