Allow nested arrays in tag rendering
Summary: There's at least one of these in phutil_tag(), and tracking them down is a huge pain, and we've made a fair number of affordances for them elsewhere which can be simplified if we just allow them to work properly.
Test Plan: Unit tests. Diff rendering in phutil_tag no longer raises warnings over hsprintf('...%s...', array()).
Reviewers: vrana
Reviewed By: vrana
CC: aran
Differential Revision: https://secure.phabricator.com/D4940