xmlrpc.inc: removed dl("xml.so")

This function has been deprecated and removed from php-5.3 and upwards,
and was only useful for PHP 4, which is not supported anymore.
xmlrpc.inc: remove deprecated xmlEntities
xmlrpc.inc: removed deprecated xmlrpc_backslash global
xmlrpc.inc: Converted $GLOBALS array to internal class Xmlrpc

This  way $GLOBALS array won’t be polluted with internal data of
us, and if something else does something to that array, it
won’t affect us anymore.