Require the "ctype" extension explicitly
Summary: Fixes T4916. Although every normal build of PHP has this in the core, at least one distribution which users could reasonably encounter does not.
Test Plan: Changed string to "ctypex", got setup warning. Changed to "ctype", got no warning.
Reviewers: hach-que, btrahan
Reviewed By: btrahan
Maniphest Tasks: T4916
Differential Revision: https://secure.phabricator.com/D8896