SELinux policies for phabricator, arcanist and libphutil

Summary:
policy source files to run phabricator with selinux enabled.

Some sites have stric selinux enforcing policies for their servers and therefore require a selinux policy to run phabricator.

Test Plan: in use on a RHEL6 system

Reviewers: #blessed_reviewers

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11035
Merge branch 'selinux'