Can't r+ all-decimal-digit commits

[arielb1]

If the relevant 7 hex-digits of a commit are all decimal (this occurs about 1 in 25 times) the commit can't be r+-ed. See for example rust-lang/rust#29408 and rust-lang/rust#29398.

[pnkfelix]

Oddly, even attempting to include the longer SHA that includes non-decimal digits does not actually work-around the problem. The only option is to say "r+" with no commit at all. :(