Add PHP openssl extension as a dependency

Summary:
After successfully installing phabricator on my Mac OS X 10.6.7, I was unable to
link my accounts to either Facebook or GitHub.

I diagnosed that file_get_contents() and fopen() were not working properly.

After installing the php openssl package I was able to get it linking
successfully.

Test Plan:
With php's openssl extension disabled, and phabricator installed. Try linking to
Facebook and GitHub and observe that it fails. You can visit the Auth
Diagnostics page and "Facebook Graph" and "App Login" should fail.

With php's openssl extension enabled, linking to Facebook and GitHub should be
successful.

Change the configuration to add "phabricator.setup = false".

Disable php's openssl extension. Visit the phabricator site and observe that it
requires you to install php's openssl extension.

Enable php's openssl extension. Visit the phabricator site and observe that it
installs fine.

Reviewed By: epriestley
Reviewers: epriestley
CC: aran, epriestley
Differential Revision: 352