The TMPDIR check implemented in a4556a73 incorrectly reports that
TMPDIR cannot hold executables on 4.3.11(1) on Ubuntu 14.04.1 LTS.
This is because a script containing no commands returns a non-zero
exit code.  Contrast the following:

  bash 3.2.53(1) on OS X 10.9.5:

    $ bash -c '' && echo SUCCESS
    SUCCESS

  bash 4.3.11(1) on Ubuntu 14.04.1 LTS:

    $ bash -c '' || echo FAIL
    FAIL

This patch modifies the test script to explicitly call `exit 0` to
ensure that a successful exit code is returned if the script executes
successfully.

Upgrade to openssl-1.0.1j

Disable insecure SSL protocols

add jruby-1.7.16

Upgrade OpenSSL library to 1.0.1i

Previous versions of the library contain several vulnerabilities:
https://www.openssl.org/news/secadv_20140806.txt

OS X: Fixes check for OpenSSL version

Fixes #606

Added definition of new rubies

Add 2.2.0-preview1

Show specific upgrade instructions based on environment

Add missing checksums to Rubinius definitions

Workaround for travis-ci/travis-ci#1719

On Fedora, this results in a nice "Fedora 19" identifier and doesn't
show the codename "Schrödinger’s Cat" which is otherwise contained in
`/etc/fedora-release`.

On Arch, this shows "Arch Linux" where previously we had no info for it
(for some reason, `/etc/arch-release` is empty).

http://www.freedesktop.org/software/systemd/man/os-release.html

Because ruby-build is both a Homebrew formula and an rbenv plugin, some
people end up with both installed. In these cases, executing
`rbenv install` vs. `ruby-build` might not use the same install. Users
end up being unsure where `rbenv install` is coming from and upgrading
it from the wrong location.

This detect whether ruby-build is contained in Homebrew or git and shows
upgrade instructions accordingly. Example:

    See all available versions with \`rbenv install --list'.

    If the version you need is missing, try upgrading ruby-build:

      brew update && brew upgrade ruby-build

`rbenv install` completion includes definitions from plugins

Before, `ruby-build --definitions` was invoked sooner than
RUBY_BUILD_DEFINITIONS was built up with paths from rbenv plugins.

[ci skip]

On FreeBSD 10, stop defaulting to MAKE=gmake

Sort Ruby versions when listing available definitions

Stable releases should now be sorted as a higher version than preview
releases or RCs. For instance:

- 1.9.3-preview < 1.9.3-rc1 < 1.9.3-p0
- 2.1.0-dev < 2.1.0-rc1 < 2.1.0
- jruby-1.7.0-preview1 < jruby-1.7.0-rc1 < jruby-1.7.0

Fixes #604

This detects when `/tmp` has been mounted with "noexec" mode and avoids
the cryptic error:

  ./configure: Permission denied

Hopefully the information provided will be enough for the user to know
that they have to change TMPDIR to another location.

It appears that regular `make` that ships on FreeBSD 10 is compatible
enough to build Rubies. This enables ruby-build on fresh FreeBSD
installs (which don't have `gmake` by default) without having to
explicitly set `MAKE=make`.

Closes #610

Now supports `-h|--help`.

This has the CI step verify the checksums for URLs that might have been
added or edited to build definitions in a pull request.