This reverts commit 23728729, reversing
changes made to 3e4547f5.

If people have `HOMEBREW_RUBY_PATH` set then things explode in a rather
confusing fashion. Instead, run `bundle` for them with the arguments
that they'd want.

Also, move `macho` requires into the module itself; it's a pain having
to do everything for Bundler before requiring `pathname` which is a core
Ruby class.

Safari uses `Mac OS X` not `OS X`. To avoid contaminating other parts of
Homebrew use a separate variable for just this part, too.

This matches what Safari does on macOS 10.12 and is generally what
tools like Google Analytics expect the format to be.

If `brew instal` is permissible, `brew uninstal` should be, too.

Users may have this set, breaking grep's output.

Fixes #1430.

November 1st 2016 has come and gone so it's time to disable this.

Also, add comments explaining why the things that have been whitelisted
have been (to avoid more being added without good justification).

This will ease user anxiety when `brew install foo' is typed but nothing
seems to happen.

These invocations occur before we can actually automatically install git via
bottle, and as such their output isn't relevant.

Small improvement to the xcode license hint. Reduces friction by allowing user to accept the license in a single step. 
Reference: http://apple.stackexchange.com/questions/175069/how-to-accept-xcode-license

If you’re using a /usr/local prefix but e.g. /usr/local/homebrew/Cellar
then you’ll miss out on most binary packages for no good reason so warn
people of that.

`Homebrew/>1.0.0 (no git repository) (Macintosh; Intel macOS 10.7.5)...)
reads pretty weirdly in a user agent and I've had complaints that `>`
may be an invalid character in some cases.

Fixes #788.

This stops `-dirty` showing up whenever you aren't in
`HOMEBREW_REPOSITORY`.

Fixes #1108.

For tagged commits produces the output:
- `1.0.1`

For untagged commits with a dirty tree produces the output:
- `1.0.1-19-g23efbc5-dirty`

Performance:
```
git describe --tags --dirty 2> /dev/null
0.07s user 0.01s system 96% cpu 0.086 total
```

This means we can tag any commit without needing to manually remember
to bump the revision every time.

To test the tag update functionality allow setting
`HOMEBREW_UPDATE_TO_TAG`.

If we have a `brew.sh` which has set
`HOMEBREW_ENABLE_AUTO_UPDATE_MIGRATION` then let's allow an auto-update
migration. That's because it contains the fix below it _before_ the
update happened which means the auto-update won't fail in the same way
as if updating from an old version.

Save the value of GEM_HOME before unsetting it,
and resetting it when setting up a gem environment.

Fixes #944.

On auto-update `HOMEBREW_LIBRARY` may change location which means that
it won't be found for the actual install command. Look for this having
occurred and then set the new `HOMEBREW_LIBRARY` (and
`HOMEBREW_REPOSITORY`) accordingly.

Not quite a mass replacement as I've used OS X and Mac OS X where
describing specific older versions and added compatibility methods
for things in the DSL.

This reverts commit 2498d99a.

It also uses `sudo` for legitimate things e.g. installing `.pkg`s
systemwide.

This seems generally like a good idea given that we're making syntax changes to
formulae & are going to keep doing so for a little while yet. Taps may have moved
over to that syntax, which then causes tap failures if brew isn't up-to-date.

Should fix situations like https://github.com/Homebrew/homebrew-php/issues/3545.

As discussed: announce that we are deprecating running Homebrew as the
root user as it's insecure and requires disabling the sandbox.

Fixes #796.

If you're using e.g. a `/usr/local/homebrew` prefix then don't require
the `/usr/local/Cellar` to be manually created to avoid e.g.
`/usr/local/homebrew/Cellar` being used. Let's do all we can to let
people use this `Cellar` location as it means they can put their
repository wherever they like and still use all our bottles.