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

This is handled by `brew style` now.

- unset IFS to fix version parsing on older Bashes
- reuse existing HOMEBREW_MACOS_VERSION if it’s available
- set rather than unset popup_stub

On older versions of OS X (i.e. pre-Mavericks) `xcode-select` is not
required to be set when using the CLT. Fix this behaviour so `brew
update` doesn't tell everyone on that configuration to `brew install
git`.

Mountain Lion: http://opensource.apple.com/source/libarchive/libarchive-25.1/config.h
  `/* #undef HAVE_LIBLZMA */`

Mavericks: http://opensource.apple.com/source/libarchive/libarchive-29/config.h
  `#define HAVE_LIBLZMA 1`

Sometimes `file` output contains data from the file under examination,
which may include binary data that does not represent valid UTF-8
codepoints. String#split dies if it doesn't understand the encoding, so
tell Ruby to treat `file` output as a bytestring.

Avoid using an unnecessary `xz` dependency when it's not needed.

Write the README but also a `.travis.yml` file (and in future perhaps a
`Jenkinsfile`).

It looks like a rebase/merge conflict remmenet.

Multiple issues have been filed about this environment variable, hence
give a warning. #932 might make this unnecessary when merged, but
hopefully this warning can be merged quickly.

ruby-macho now performs all relocations in Homebrew.

Additionally, delete the defunct CctoolsRequirement.

It's not used on enough configurations now that there's little point in
keeping it around. See e.g. `:autoconf` for prior art.

This was omitted from #1258, incorrectly fixed in #1267, reverted in
 #1268 and re-applied in this commit.