Skip upgrade of pinned dependency if it's outdated

README and ISSUE_TEMPLATE: quote $(brew --repo)

dev-cmd: add `--help` to all developer commands.

docs: Explain Tab instantiation

Warn when changing branch on update

Also, flag those that we never want to be in a manpage.

This was really confusing to me, and I had to go looking through the Tab
history, where I found a comment explaining it that has since been
deleted. This wasn't a great experience.

This commit basically adds that explanation back in.

This reverts commit 2498d99a.

Forbid to install formual if it has pinned dependencies.

Prompt user to unpin pinned dependencies of the formula

Always a good idea to quote command substitution.

test-bot: separate tap/core no formula handling.

`e.tap` calls the tap method which wants a block on
`FormulaUnavailableError` so the previous approach is .

test-bot: handle missing tap in exception.

Handle the case where a `FormulaUnavailableError` does not contain a tap
reference so fall back to `CoreTap` in this case.

xcode: die unless Xcode/CLT up-to-date on prerelease macOS

test-bot: put exception, retry on missing formula.

Better use the abstraction layer so e.g. Linux could have similarly
fatal checks for these things.

This will be useful in debugging (and recovering from) the situation
where sometimes formulae can't be found when specifying multiple on the
command-line.

update-report: also link docs, completions.

minor typo

Fixed minor typo -- missing preposition.

test-bot: tweak cleaning behaviour again.

Always run `git clean -ffdx` on HOMEBREW_REPOSITORY. Also, ensure that
if we can't find a formula that's logged.

test-bot: git clean less in cleanup_*.

These are more files in the HOMEBREW_REPOSITORY that we want to link to
the HOMEBREW_PREFIX.

Pull more logic into the more generic `link_src_dst_dirs` to be used to
do more linkage.

There's edge-cases which is breaking tap CI.

Add `cask_files` method to `Tap` class.

Catch system libressl in openssl audit as well