`brew uses foo bar` is supposed to return the intersection of formulae
that use foo and bar. However, this was broken by changes made to
support requirements that can coerce to regular dependencies.

With that option iterate only over `Formula.installed`, otherwise
iterate over `Formula`. This is faster than iterating over all the
formulae and checking if it's installed.

Fixes Homebrew/homebrew#27259.
Closes Homebrew/homebrew#27295.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Closes Homebrew/homebrew#24145.

Closes Homebrew/homebrew#23758.

Fixes Homebrew/homebrew#20819.

Fixes Homebrew/homebrew#17074.
Closes Homebrew/homebrew#17075.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>

Deprecated Formula.all, replaced usage with more appropriate enumerable options. Just check out how much nicer `brew audit` runs now.

Closes Homebrew/homebrew#8870.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Passing a `Proc` doesn't work in Ruby 1.8.6 which causes `brew uses` to fail on
Leopard.

The code was sucking. To the extent that maintenance was hard. It's a lot
easier to work with code that is sensibly split at sensible boundaries. So
now it is more like that.

But the refactor is minimal. Because we don't want you to have more merge
hell than absolutely necessary.

If you merge you will need to pay attention to brew.h.rb (as it is deleted)
and bin/brew (as command logic is gone). It will be painful, but you will just
have to help git out by moving any changes around manually.

Note compatibility.rb. It ensures that any function renames or removals don't
break anything. We're pretty serious about backwards compatibility. And that's
because we encourage you to hack around with the innards. And we couldn't do
that if we would then just make stuff disappear behind your back.