[PATCH 0 of 6 DRAFT] Work to add time based progress with convert as example

[timeless]

This patch series was done in conjunction w/ durin42.

The series is known to include some test failures.

The general idea is that one can use hg convert or hg recover and get a time
estimate for long operations (both convert and recover are quite long).

It will look something like this:
converting [================================>                    ] 1502/2361 0:18
- where time is in h:mm.

durin42 will resend a unified series including both of our work.