travis: fast finish builds.

Preserve link status on reinstall/upgrade.

formula_installer: use default_formula for bottles

Fix trash script.

Show failing Linux builds (which run much more quickly) before the macOS
build has completed.

https://docs.travis-ci.com/user/customizing-the-build/#Fast-Finishing

This was the original, intended functionality before this was broken
in fe117bf7.

Fixes https://github.com/Homebrew/homebrew-core/issues/13680.

Enable more deprecations.

This means if a user has manually `brew unlink` or `brew link --force`d
something then that status will be preserved after they `brew upgrade`
or `brew reinstall` that formula.

This generally should make things that are keg-only by default easier
to swallow.

formula_support: add provided_pre_high_sierra keg_only

formula_installer: simplify callers.

keg: correctly cleanup old aliases.

sandbox: sandbox all taps by default.

Use `mktmpdir`.

Cleanup after each Cask.

Silence all specs by default.

installer_spec: silence test output.

There's a bunch of duplication going on that's not really necessary.

Cleanup old, versioned aliases and tap aliases folders when unlinking
or uninstalling a keg.

audit: Run style violations check when `--new-formula` is passed

Don’t output Caskroom creation messages on non-TTY.

formula_installer: allow version mismatched build deps

Use https for all docs.brew.sh links.

Only check runtime dependencies for version conflicts to avoid
having to create unnecessary duplicate formulae.

For example, a formula that needs to be built with ghc@8.0 should still
be allowed to have a build-time dependency on a cabal-install that was
itself built with ghc@8.2.

May as well use the more secure link when possible.

https://github.com/Homebrew/homebrew.github.io/pull/171

OS: use RbConfig instead of RUBY_PLATFORM

High Sierra: updates for Beta 4 et al.

`RUBY_PLATFORM` is always `"java"` when running JRuby, no matter what is
the underlying platform.

See also https://github.com/pry/pry/issues/386.