Merge branch 'rs/nth-parent-parse'

Merge branch 'rs/nth-parent-parse'

The object name parser for "Nth parent" syntax has been made more
robust against integer overflows.

* rs/nth-parent-parse:
  sha1-name: check for overflow of N in "foo^N" and "foo~N"
  rev-parse: demonstrate overflow of N for "foo^N" and "foo~N"