I think it is important to mention that some distributions apply bugfixes for older versions so "Available since PHP 5.3.9" is not reliable, for example:
debian squeeze implemented the directive max_input_vars in PHP 5.3.3-7+squeeze7 (see http://ftp-master.metadata.debian.org/changelogs/main/p/php5/php5_5.3.3-7+squeeze17_changelog )