comment/todo re: directory creation
show staging directory (caskroom) in doctor

refs #6471
Validate value of GPG :key_id

The value of `:key_id` must be an hexadecimal string of length 8, 16,
or 40.
Update GPG tests to use valid key IDs
Test for invalid GPG key IDs
User-friendly error messages for invalid options/arguments; fixes #5997

- Show a more user-friendly error message when dealing with an option whose (mandatory) argument is missing.

- Likewise, we show a more user-friendly error message when a given option is ambiguous. Examples:
    - Given `-f`, the parser successfully expands to `--fontdir`.

    - Given `-c`, we fail to expand because the parser can’t tell if the user means `--caskroom` or rather `--colorpickerdir`. This exception now results in a nicer error message.

- Some commands now result in a consistent error message when a required cask name is missing.
This affects all stable commands which require one or more cask names as arguments, i. e. `cat`, `create`, `edit`, `fetch`, `info`, `install`, `uninstall`, and `zap`.

- Up to now, the commands `cat`, `create`, `edit`, and `info` used to treat any unknown option as a cask name. This commit changes that behaviour to make it consistent to the rest of the commands (like `fetch`, `install`, `uninstall`, and `zap`), who have silently discarded any unknown option in the past, and continue to do so.
Add tests for #5997
Rewrite tests to make them work with Ruby 1.8
Bring the repo test back in sync with `.gitignore`.

This keeps the tests from failing, e. g. when developers use `rbenv` to run the 1.8-based tests.
Add Tableau.app
Add Tableau Public.app
Merge pull request #6496 from ianks/tableau-public

Add Tableau Public.app
Merge pull request #6495 from ianks/tableau

Add Tableau.app
added imazing (replaced diskaid)
Merge pull request #6498 from vitorgalvao/imazing

added imazing (replaced diskaid)
Update playonmac to 4.2.5.
Merge pull request #6499 from hswong3i/feature/playonmac-4.2.5

Update playonmac to 4.2.5.
Merge pull request #6493 from claui/fix-repo-layout-test

Bring the repo layout test back in sync with `.gitignore`
Upgrade Shortcat to 0.7.4
Merge pull request #6503 from crainiarc/shortcat

Upgrade Shortcat to 0.7.4