Implement ability to find repository directory in a parent directory

* Ability to find repository directory in a parent directory is turned on
  automatically if `-r' not given and only one (or no) directory given.

* User can specify `-F' when providing more than one directory, however `-r' may
  not be used.

* Several fixes introduced, mainly cosmetic.

* `check_dir' no longer returns a string and now uses a global variable due to
  the current working directory not updating upon its return.