A hacky way to run all the builds in the travis "matrix".

Not currently loading `.travis.yml`.

Found I had to additionally ignore `Gemfile.minitest.1.4.1` and
`Gemfile.test-unit.latest`. Not sure why I had to do the former, but the
latter is because a new version of `test-unit` is out which is currently
not supported by `mocha`.

build-matrix.rb

@@ -0,0 +1,49 @@
+#!/usr/bin/env ruby
+
+def execute(*commands)
+  commands.each do |command|
+    system(command)
+    unless $?.success?
+      message = [
+        "Executing shell command failed.",
+        "  Command: #{command}",
+        "  Status:  #{$?.exitstatus}"
+      ].join("\n")
+      raise message
+    end
+  end
+end
+
+def reset_bundle
+  execute(
+    "rm -rf .bundle/gems",
+    "rm -rf gemfiles/.bundle/gems",
+    "rm -f *.lock",
+    "rm -f gemfiles/*.lock"
+  )
+end
+
+def run(gemfile)
+  ENV["BUNDLE_GEMFILE"] = gemfile
+  ENV["MOCHA_OPTIONS"] = "debug"
+  reset_bundle
+  execute(
+    "bundle install --gemfile=#{gemfile}",
+    "bundle exec rake test"
+  )
+end
+
+EXCLUDED_MINITEST_GEMFILES = [
+  "gemfiles/Gemfile.minitest.1.3.0",
+  "gemfiles/Gemfile.minitest.1.4.0",
+  "gemfiles/Gemfile.minitest.1.4.1",
+  "gemfiles/Gemfile.minitest.1.4.2",
+  "gemfiles/Gemfile.test-unit.latest",
+]
+
+reset_bundle
+Dir["gemfiles/Gemfile.*"].each do |gemfile|
+  next if (RUBY_VERSION == "1.9.3") && EXCLUDED_MINITEST_GEMFILES.include?(gemfile)
+  p [RUBY_VERSION, gemfile]
+  run(gemfile)
+end