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.

On FreeBSD, use the same approach as OS X with `sysctl`.

Make build output and log more useful

Fix `rbenv install --list` for definitions auto-discovery

The build definitions auto-discovered from rbenv plugins would
previously not appear in `--list` results due to discovery process
taking place too late.

`assert_success` doesn't accept an argument via stdin

This is useful info for when someone is pasting build output to our
issue tracker seeking support.

People often miss that and think that the last 10 lines of build output
is the only information they got.

Since `./configure` executes in a bash subshell, it failing would
execute the ERR trap twice: once in a subshell and once in the main
process. An explicit `return 1` skips one of these ERR traps and fixes
double output.

I hope.

[image of I Have No Idea What I'm Doing dog]

This might save us from having to ask people which version they have
installed when they paste us build output from the console.