Although `sandbox-exec` is available in 10.5, it has very limit
support on the DSL for sandbox profile file(.sb file). Therefore,
sandbox for Homebrew on 10.5 is broken.

Closes #735.

Signed-off-by: Xu Cheng <git@xuc.me>

Temporarily.

brew.rb: allow 10.5.

test-bot: tap cask before cask-tests.

`Hardware.is_32_bit?` is deprecated.

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.