When exactly two versions of a package were installed, the uninstall
message should not read "Remove them all with...", since only one
version remains.

"Remove all versions with..." is flexible enough to avoid being
interpreted as grammatically incorrect, and it still accurately
describes the general behavior of `brew uninstall --force`.

update.sh: tweak tag handling.

- Don't let the `UPSTREAM_TAG` variable bleed into future repository
  checks.
- Even if the tag branch is an ancestor of the tag ensure that it's
  forced back to the tag anyway.

readme update: it's version 1.0 already

update.sh: update to latest Homebrew/brew tag.

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

Rather than following every change on `master` let’s have non-developer
users (i.e. those who have never run a `dev-cmd` or set
`HOMEBREW_DEVELOPER`) update between tags.

This provides a fairly natural beta (the `master` branch`) and stable
(the tags) approach without restricting us to any particular way of
managing our tags.

PULL_REQUEST_TEMPLATE.md: Fix CONTRIBUTING.md link

Update: ensure tags are fetched

Update `brew-cask` man page and simplify `brew man`.

We use these for updating people who just follow tags.

Closes #1040.

Rearrange repository

Readme tweaks

update-report: migrate on newer auto-update.

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.

test-bot: always set PATH to HOMEBREW_PREFIX.

Set the `PATH` to always have the `bin` and `sbin` for the current
`HOMEBREW_PREFIX` at the beginning.

os: update Linux troubleshooting url

No auto update migration

os/mac: mark Mavericks as outdated.

Use user GEM_HOME for installing gems

Save runtime dependencies in INSTALL_RECEIPT.json