Fix "undefined symbol: stream_printf" for PHP 5.5

He,

thanks a lot for the extension!

Building it under PHP 5.5. worked but loading it failed for me:

> Warning: PHP Startup: Unable to load dynamic library '/usr/lib/php5/20121212/meminfo.so' - /usr/lib/php5/20121212/meminfo.so: undefined symbol: stream_printf in Unknown on line 0
PHP 5.5.8-3+sury.org~precise+2 (cli) (built: Jan 29 2014 13:23:55) 

so I've looked around a bit and it seems that `php_stream_printf` should work out.

It runs with my 5.5. build now but i didn't do testing on other versions.