We'll keep the Homebrew installer pointing to Tigerbrew for now but as
Homebrew/brew technically has no reason to not work on 10.5 let's remove
this check.

Fixes https://github.com/Homebrew/homebrew-core/issues/3973.

Set -no_weak_imports linker flag for Xcode 8

Assume Ruby 2

Remove legacy Aliases/Formula symlink from Library

Prepare for Homebrew Cask to be imported.

- ignore Cask's files in `readall` (for now, there's an intentional
  syntax error that will need fixed)
- run Cask's tests if they exist
- don't check Cask's files in coverage reports (for now)

Tweak HOMEBREW_DEVELOPER documentation.

diagnostic: don't barf if HEAD is also a file.

Enable sandbox by default for homebrew/core

This option does more than just print warnings so let's make a more
generic description with a more specific example.

Closes #716.

- Inconsistent or unneeded indentation
- Missing or superfluous empty lines
- Missing or wrongly formatted arguments in command summary
- Missing punctuation

Closes #694.

tests: add cmd/audit unit tests

list: note that `ls` command is used.

Enable vendored Ruby 2.0.

Add a new `Sandbox.formula?` method to see if a given formula should be
sandboxed. Use the formula to check its tap against a list of
pre-approved taps where we know every formula builds under the sandbox
(currently just homebrew/core).

Simplify checking if we’re going to sandbox a test with `Sandbox.test?`.

brew: sanitize BASH_ENV