On OS X and some other platforms it doesn't matter, as `tar`
automatically detects the compression method, but on platforms that
don't it's important to declare the archive format. For ordinary
tarballs the extension provides this info, but since Topaz archive
doesn't have an extension in the URL, we add a fake one via a dummy
query string parameter.

Fixes #357

I thought this was not necessary, but a number of people had problems
when linking to OS X's "readline" (actually Editline wrapper):

- Some components of Pry wouldn't work
- Writing literal Unicode characters was not possible #379
- The compilation would downright fail in some cases #82 #461

Fixes #461

Install the missing `rubysl-tracer` gem

References rubinius/rubinius#2780

We symlink Rubinius' `PREFIX/gems/bin` into `PREFIX/bin` so that new
RubyGems binstubs get added to the main bin directory and therefore
become available to rbenv.

However, by throwing away `irb`, `rake`, `rdoc`, and `ri` binstubs
during this process (which are non-executable and have an invalid
shebang), we break the same commands in latest versions of Rubinius.

This change ensures that these binstubs get preserved, their shebang
corrected to `#!PREFIX/bin/rbx`, their executable bit flipped on, and
copied over to the main bin directory.

Fixes #468

Add JRuby 1.7.9 to rbenv

Add definition for heroku-patched 1.8.7-p375

This build is an unofficial backport of the patch for
"Heap Overflow in Floating Point Parsing (CVE-2013-4164)"
to Ruby 1.8.7-p374.

The defnitoin refers to a tarball of this tag:
https://github.com/heroku/ruby/releases/tag/v1_8_7_375

Ref. #458

Cf. https://github.com/sstephenson/ruby-build/commit/50bf60f9c2510fbee7f111046e97fe8bf9e66472

Update 2.1.0-preview2

Typo fixed

Fixes #429, references rubinius/rubinius#2693

Adds ruby 1.9.3-p484 and ruby 2.0.0-p353 definitions

Add rbx 2.2.0 and 2.2.1 definitions.

Add definition for jruby-1.7.8

Add a definition for JRuby 1.7.7

`grep -c` would correctly output "0", which is handled specially later
on, but would also exit with a nonzero status which would abort the
script. Piping the output to `wc` to do the counting makes the exit
status of grep irrelevant.

Fixes #447

References #443

Makes sure that installing Rubinius won't touch other gems outside the
build directory.

Installing Rubinius would print "BUILD FAILED" at the `bundle` step but
the installation would proceed nevertheless and finish successfully.

It turns out that the `command ...` expression will trigger the ERR trap
on failure even when it's a part of `||` list or a condition inside an
`if` statement. This defies how the ERR trap is supposed to work, so the
workaround is to execute it in a subshell which doesn't inherit the ERR
trap of its parent.

This is a regression introduced by
d13ae0ad

References #267

If a commit introduced a new Ruby definition, we want it mirrored even
if there might have been an accidental failure on CI.