Homestyx hydra

R1:786b135a662c

variable days back for `bin/mail volume`

Summary:
Email is so exciting I can't wait 30 days for initial results.

ref T9161

Test Plan:
* `./bin/mail volume --days 60` took longer and gave plausibly larger
results.
* `./bin/mail volume --days 0` quickly told me no mail had been sent.
* `./bin/mail volume` Said it was still looking 30 days back.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Maniphest Tasks: T9161

Differential…
Repository: R1 hydra
Commit Date: Aug 27 2015