R1:9b043e59668c

Bump required PHP version

Summary:
`mysql_set_charset()` is available since PHP 5.2.3.
I've searched also for other new functions and this is the newest.

Test Plan: /

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D2126