Install the latest Ruby from:
https://github.com/Homebrew/homebrew-portable-ruby/pull/55

This updates ncurses and openssl as well as more closely matching the
Apple's ruby build options.

Notably, this includes the DBM support needed for #3720.

components_redundancy_cop: make non-strict

urls_cop pypiurls: make non-strict

components_order_cop: make non-strict

Shorten some links in README.md

Support enabling auto-updates for non-GitHub taps

linkage: fix --test exit code.

Ensure that a non-zero exit code is set both for missing random dylibs
and random missing dependencies.

Additionally, while we are here, drastically trim down the public
interface for this class to the bare minimum and allow getting the
output from `display_test_output` as a variable.

Fixes issue mentioned by @ilovezfs in:
https://github.com/Homebrew/brew/pull/3940#issuecomment-383794520

Fix `MissingFormula` namespacing.

Refactor and fix style for some specs.

x11_requirement: move download to base class.

formula: sort aliases in to_hash.

No reason to have it in macOS class and keeps consistent output with
`brew info` on Linux.

Otherwise the ordering varies based on the filesystem.

requirements: define cask on base class.

The `cask` attribute doesn't make as much sense on Linux but can be
ignored there. The advantage of this change is that (like #4086) it
allows figuring out the relevant cask for a formulae requirement on a
Linux machine.

formula: tweak to_hash bottle output.

AbstractDownloadStrategy#safe_system : Don't splat 2nd arg to ErrorDuringExecution::new

Make some changes required to have `brew info --json=v1` whether there
is any bottle block rather than a bottle checksum for the given system.

This provides more consistent output.

Xcode 9.3

Fixes #4084.

formula_support: deprecate more keg_only reasons.