CodeIgniter behavior change - $_POST and global_xss_filtering config

The default behavior is all variable including $_POST is first sanitize
with calling _sanitize_globals() from constructor. Then it will be
impossible to get raw data from $this->input->post('var', FALSE) when
global_xss_filtering is set TRUE.

This change will disable global sanitazion for $_POST variable, thus
enable/disable it per request.
Cleaning input on kserialize() and kunserialize()
fix kunserialize() and kstripslashes() helper
Clean site config data for saving to database, especially for html value