Include previous day's builds in potential inbound range

Starting from the current nightly revision may not be good enough, as there
may have been commits to inbound between the time yesterday's nightly was
built and the last time that m-c commit was merged into inbound.

(this solution is not perfect either but it should work for 99% of cases)

https://bugzilla.mozilla.org/show_bug.cgi?id=962742