Allow phutil_render_tag() to accept an array content argument

Summary: D4509 converted some phutil_render_tag('x', array(...), $x.$y) to phutil_tag('x', array(...), array($x, $y)), but we don't currently support this. Support it, since it makes conversions easier.

Test Plan: Fixes some issues in the phutil_tag branch, like PhabricatorPropertyListView.

Reviewers: vrana

Reviewed By: vrana

CC: aran

Differential Revision: https://secure.phabricator.com/D4640