Add setup warnings for "local_infile" (MySQL Server) and "mysql[i].allow_local_infile" (PHP Client)

Summary: Ref T13238. Warn users about these horrible options and encourage them to defuse them.

Test Plan: Hit both warnings, fixed the issues, issues went away.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13238

Differential Revision: https://secure.phabricator.com/D19999