Merge branch 'bc/rev-parse-path-format'

Merge branch 'bc/rev-parse-path-format'

"git rev-parse" can be explicitly told to give output as absolute
or relative path with the `--path-format=(absolute|relative)` option.

* bc/rev-parse-path-format:
  rev-parse: add option for absolute or relative path formatting
  abspath: add a function to resolve paths with missing components