Rationale: some software (e.g. GNU Coreutils, GnuTLS 3.x), have started
distributing _only_ xz-compressed tarballs. There is no system XZ
utility provided by OS X, but it is necessary so that we can continue to
provide formulae for this software.

If XZUtils isn't installed, we abort and prompt the user to `brew
install xz`.

The `xz` command itself doesn't do any untarring, so we write the
decompressed archive to stdout and pipe it to tar.

Commit dec4b73aa0 ("Allow `brew update --rebase`") changed the format of
the `git pull` command slightly, introducing an extra space (to allow
for the --rebase option), so let's update the test expectations for this.

We still need to write tests for '--rebase', but in the meantime they
once again pass for the normal case.

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

Commit 2695821e98 ("Only use the bottle if its version is up-to-date")
essentially broke the ImageMagick bottle, because the version parsing
logic returns "1" as the bottle version.

Fixing this requires only a slight modification to the bottle URL regex;
includes a test.

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

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

I inadvertently gzipped it last night. That in itself doesn't cause any
tests to fail because the download strategy code is robust, but it's
fixed here anyway to be consistent. Basically, I'm dumb.

I also took the opportunity to remove the other resource fork file, so
the tarball is clean.

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

The test_a_basic_install was failing because it expected
libexec.children.length to be 1, when in fact there were two files in
the untarred libexec: NOOP, and the Mac OS X resource fork file ._NOOP.

That file is now removed, and the test passes.

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

The tests for update have been neglected during the last few rounds of
changes, so fix them up.

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

Consequence: you can no longer install when something is already installed, you must upgrade it. This doesn't apply if the formula in question was unlinked. You can still --force installs though.

Rationale: the old way of installing over the top would leave symlinks to multiple versions in /usr/local if the old version had a file the newer version didn't. The new upgrade command handles everything properly.