Improve the messaging around `brew install` when there's a possible user
action such as an `upgrade` or `link` and don't tell people to
`install --force` when it's unnecessary.

While I did this, tweak the output and function usage in a couple of
related places.

Some example output before this change:
```
Warning: openssl is a keg-only and another version is linked to opt.
Use `brew install --force` if you want to install this version
Warning: mysql@5.6 is a keg-only and another version is linked to opt.
Use `brew install --force` if you want to install this version
Warning: analog-6.0_1 already installed
Warning: bash-completion@2-2.5 already installed, it's just not linked.
```

Some example output after this change:
```
Error: openssl 1.0.2k is already installed
To upgrade to 1.0.2l, run `brew upgrade openssl`
Warning: mysql@5.6 5.6.36_1 is already installed
Warning: analog 6.0_1 is already installed
Warning: bash-completion@2 2.5 is already installed, it's just not linked.
You can use `brew link bash-completion@2` to link this version.
```

Use Python's flock instead of Ruby's

Deprecate `--caskroom` flag.

Fix cli default options.

Vendor compatibility fixes

Relocate virtualenv orig-prefix

This works around older versions of `which`, which return a
string on failure.

Ruby first gained flock in 1.8.7, which is a problem since we're using
this lock utility in `vendor-install` in order to install a newer Ruby.

Fortunately, Python 2.3(!) has flock support.

Fix `uninstall` order.

Add `SUDO_ASKPASS` to `brew-cask` manpage.

Fix `previous_version_and_checksum` method.

Fix appcast checkpoint command.

Refactor `CLI`.

patch: clean up with Forwardable

audit: fix versioned alias errors in homebrew/core introduced in a7c6a57c