Closes Homebrew/homebrew#17618.
Closes Homebrew/homebrew#17813.

a6324cb forget fix soft link in ENV folder, it cause superenv
use Apple provided git and svn.

Closes Homebrew/homebrew#17927.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

The form "attr :name, true" is deprecated and causes Ruby to emit a
warning in verbose mode. Using attr_{reader,writer,accessor} is more
clear anyway, so do so.

Make it no longer possible to override e.g. `brew install` with a
script if there is already a built-in Homebrew command named
`brew install`.

References Homebrew/homebrew#17673

Closes Homebrew/homebrew#17843.

Closes Homebrew/homebrew#17814.

Local changes to the cached repository should not cause fetch or install
to error out.

Otherwise, if the local branch is behind the remote branch, or has
diverged, we will stage the wrong revision.

Closes Homebrew/homebrew#17852.

Fixes Homebrew/homebrew#17866.

When we are building from a tag, and that tag is already present in the
cached repository, we don't to hit the network; everything we need
already exists.

Closes Homebrew/homebrew#17805.

The name attribute of requirements is used when generating options for
the :optional and :recommended dependency tags.

Unless otherwise specified, the name attribute of a Requirement will be
populated by stripping any module prefixes from the beginning and
"Dependency" or "Requirement" from end of the class name and downcasing
the result.

Closes Homebrew/homebrew#17759.

This code only existed to support very old formula syntax, which was
otherwise removed in e6b97bebd99779b52462dcd387191d804fc95b93.

c.f. Homebrew/homebrew#17772.