diagnostic: check if the user is a member of the admin group.

exceptions: better handle unsupported macOS versions.

Non-administrative users are unable to run `brew linkapps` (and possibly other
commands) under normal circumstances.

cask: Delete package dir if it is symlink on the uninstall

Fix broken link

Don’t fail on `OS::ISSUES_URL` being missing (which happens on
unsupported macOS versions) and instead tell people to not file issues.

Do not remove unknown bottle tags

osxfuse_requirement: add library and include paths

audit: allow deprecated options on new @ formulae.

As these may be migrations from another tap where we want to migrate
options across correctly.

In the installation whose prefix is other than /usr/local,
osxfuse library and include path must explicitly be specified during build.
Although brew's pkg-config is configured to prepend appropriates paths,
the prepended paths (/usr/local) supercede the original HOMEBREW_PREFIX.
This behavior will cause the linker to select libraries outside brew's tree.

By adding /usr/local to HOMEBREW_LIBRARY_PATHS, superenv ensures that appears
only after the HOMEBREW_PREFIX, and thus fixes this problem.

HOMEBREW_INCLUDE_PATHS is also configured like keg-only Formulae.

compat: deprecate Utils::JSON in favor of corelib JSON.

When a Formula is converted into a Cask (e.g. osxfuse),
a symlink remains at the place of package dir.
This change ensure to remove such leftovers.

Load cask file in `.metadata` directory directly.

Cask: Add the choices option to pkg stanza

LLVM Clang fixes

We can filter it just for Clang and let it be used by anything else.

This was implemented before the rest of the file was refactored.

A more widely used style than relying on `if`/`else` returns.

This makes it easier to identify null versions when inspecting them.

audit: check formula name against blacklisted names.

Prefer brewed Clang over gcc-6 for needs :openmp

install: suppress redundunt warnings with `depends_on` requirement

Remove kernel extensions specified in `uninstall :kext`.

installer command accepts -applyChoiceChangesXML option to change
customize options on the GUI installer from the commandline.
(`man installer` for more detailed information)

The introduced option `choice` enables the choice changes to be supplied
via pkg stanza without tricks in preflight code.

When a formula depends on any requirements, they evaluated at most three times:
before locking, before installing dependent, before building formula.
When a non-fatal requirement is specified and thus evaluated three times,
mostly the same warning message is also emitted three times.

This change restricts printing the warning messages only when a bottle is
successfully installed or before building.
Since this timing is after the final dependency computation for each cases,
the warnings will be most useful to check what is not yet satisfied.

Fix flaky tests.