Merge branch 'kh/replay-invalid-onto-advance'

Improve the error message when a bad argument is given to the
`--onto` option of "git replay".  Test coverage of "git replay" has
been improved.

* kh/replay-invalid-onto-advance:
  t3650: add more regression tests for failure conditions
  replay: die if we cannot parse object
  replay: improve code comment and die message
  replay: die descriptively when invalid commit-ish is given
  replay: find *onto only after testing for ref name
  replay: remove dead code and rearrange