Used in trying to use a `Jenkinsfile`.

bottle: set bottle block tap.

Fix Library/Homebrew/language RuboCop warnings

Avoids issues when using `—keep-old`

cask/cli/cleanup_spec: comment out flaky test.

test-bot: don't try to `git clean` any taps.

This has been causing sporadic CI failures.

Also, unify the cleanup code and be more careful and consistent with
untapping.

test-bot: try again to fix homebrew/core untap.

Be more selective with the `git clean` and remove the broken attempt
to autotap if missing (as it'd be slow anyway).

test-bot: --ci-upload can upload from current dir.

Look in the current directory rather than only allowing upload from
Jenkins.

Call subcommands from zsh completion

bottle: fix old_value/value ordering for --merge.

Previously this was the wrong way around causing it to not be accepting
enough on e.g. a bump from :any to :any_no_relocation.

bottle: use key/value rather than field.

Consistent naming is good.

Sierra: update diagnostic message, pkg-config, Xcode doc

bottle: further improve --keep-old mismatching.

- Make the code more similar between `bottle` and `bottle --merge`.
- Also output the mismatched values when using `--merge`.

tests: always set HOMEBREW_DEVELOPER=1.

Merge Cask's gitignore with root one.

bottle: improve --keep-old failure output.

If fields have changed: tell the user what they were before and are
afterwards.

This fixes the ignoring in libgit2 clients that don't read nested
`.gitignore` files.

Unit tests should be run consistently no matter who is running them and
we can stub `ARGV.homebrew_developer?` if we need to change them.

Add language method to `OS::Mac`.

diagnostic: remove duplicate checks.

Don't require/recommend ownership of /usr/local.

Set HOMEBREW_DEVELOPER automatically

Apple reset this on every OS X major (and some minor) updates and it
always proves a painful and unnecessary step. Instead just check the
directories we actually care about are writable.

This may mean if these directories do not already exist (although they
are now created by the installed) that `brew link` will fail and require
manual intervention but this seems to be superior for both new and the
majority of existing users.