Update documentation of brew install syntax to match its actual behav…

integration_test: try tests on Gem load failure.

tests: unpin bundler.

This should help with debugging `Gem::LoadError`s (e.g. for
https://github.com/Homebrew/homebrew-test-bot/pull/111).

These issues were fixed by https://github.com/Homebrew/brew/pull/2872
and https://github.com/Homebrew/brew/pull/2823.

brew.sh: always use 7 chars for HOMEBREW_VERSION.

This avoids inconsistency based on Git versions.

python_virtualenv_constants: update virtualenv to 15.1.0

Revert "FileUtils.make: don't bypass superenv"

fix link to Interesting-Taps-and-Forks.md

This release adds support for Python 3.6, the current python3
version in homebrew/core.

High Sierra: updates for DB3 et al.

Call upgrade if something was passed to update

sandbox: allow write access to /dev/random

This avoids build failure for `root6`.

MacPorts currently avoids the failure with a patch, as their sandbox
doesn't yet allow write access to `/dev/random` either:
https://github.com/macports/macports-ports/blob/7792b2c5655f9d2adb979434a242cc3ac60fea40/science/root6/Portfile#L73-L75
https://github.com/macports/macports-ports/blob/7792b2c5655f9d2adb979434a242cc3ac60fea40/science/root6/files/patch-disable-hsimple-macro.diff

The relevant code where `/dev/random` is opened with `O_WRONLY` is here:
https://github.com/root-project/root/blob/15673deba5a0cb73d90ae8f36d7b010f65b5e96e/interpreter/cling/lib/Utils/PlatformPosix.cpp#L63-L82

So the user could just copy-paste the command.

Acceptable-Formulae: general cleanup.

- We no longer care about dupes, really
- Extend `.app` criteria to include GUI applications in general
- Note we want things to build with Clang
- Note we don't want users to have to faff too much

Fix `brew tests` on High Sierra.

Don't add these unconditionally or with Bundler to speed things up a
bit. Also, to speed things up further cache these arguments so we don't
have to do the same generation every time.

Add example links in “Python for Formula Authors”

FileUtils.make: don't bypass superenv

audit: Port audit_conflicts method to rubocop and add tests

spec_helper: add focus support.

When adding `, :focus` as a trailing argument to a `describe` or `it`
this allows you to only run that single test.