Improve libphutil compatibility on Windows

Summary:

• Disable ANSI terminal codes, since they don't work.
• Fix various path/directory things that are different on Windows (absolute paths are C:\..., paths are \thing\thing).
• Remove assertAbsolute() which has no callsites.
• Use getcwd(), not ENV['PWD'].
• Don't try to set streams blocking. "Hopefully" this only makes things run slower (nonparallel) and reduces the resolution of timeouts.

Test Plan: Made it most of the way through some commands on Windows.

Reviewers: btrahan, Makinde, Koolvin

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T124

Differential Revision: https://secure.phabricator.com/D1757