formula_installer_spec: add default formula test.

audit: check for unversioned formulae.

Update all references to taps.

Add `Container::Executable`.

audit: Fix cctools invocation check regular expression.

Additionally, ignore the cctools formula itself, since it obviously
needs to check cctools invocations.

Test the situation where a requirement is satisfied by a non-formula
but the `default_formula` is also installed.

audit: Check for invocations of cctools.

diagnostic: increase minimum git version to 1.8.5

diagnostic: check homebrew/core git remote.

update-test: improve error handling.

older versions do not support the 'git -C <path>' option

Fail if the start or end commit are missing and retry finding the
previous tag by fetching all tags if they are missing.

This should fix CI on the current Homebrew/brew `master` branch.

Closes #2404.

audit: bump whitelisted elm-format version to 0.6.0-alpha

If we're adding a versioned formulae we want to ensure that there's also
an unversioned one too.

Check the remote for homebrew/core as well as homebrew/brew as we've
seen a few cases (e.g. #2387) where it was misconfigured.

While we're here, tweak the messaging to tell people what to do and how
to do so with a single command.

updating the exception for "kibana" for the "@" naming scheme. File changed: audit.rb

- Remove taps that are (or will shortly be) deprecated.
- Remove commands that are only relevant to the boneyard (which will
  shortly be removed).

vendor: Update ruby-macho to 1.1.0.

docs: code example reformatting

Add labeled fences to most code blocks, monospace terms where
appropriate, omit "$" when referring to variables

Also works around bug in Jekyll where a URL with a "#" will cause links
in the same paragraph to not have their extensions replaced by using
"#" instead.

pull: warn (not die) on bottle publish failure.

formula_installer: tweak req formula additions.

Rather than just checking if a requirement's dependency is installed or
not check if the requirement was actually satisfied by a particular
formula rather than e.g. just having a `default_formula` defined.

New-Maintainer-Checklist: be more explicit.

README: add some more shields.

migrator: allow new cellar to exist already

gpg: add GnuPG series 2.1.x to supported versions

Lets us migrate a formula to a name that may have previously been used.

If gnupg 1.x is installed as "gnupg" and gnupg 2.x is installed as
"gnupg2," it's currently not possible to rename gnupg2 -> gnupg, since
the 1.4 keg will already be installed in the "gnupg" Cellar, so in order
to reclaim the name "gnupg" to be used for 2.1, either 1.x must be
manually uninstalled, or the new cellar needs to be allowed to exist
already.

link: tell users of `brew link --force` about opt.