Let `phutil_rebuild_map` show a progress bar

Summary: .. Instead of dots that are hard to count.

Test Plan: remove `.phutil_module_cache` and do `arc liberate`

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9584