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"

diff --cc sha1-name.c
Simple merge

diff --cc t/t1506-rev-parse-diagnosis.sh
Simple merge