a test that tries to run two builds at once
Updates to the new systemjs

This updates us to the latest systemjs as is merged in bitovi/systemjs.
All tests passing.  One change that is possibility controversial:

SystemJS no longer supports the `__useDefault` option in es6 modules to
import into non-es6 formats as the module's value. Instead any non-es6
module that imports an es6 module can use use it's `default` property.
Updates to SystemJS 0.8.2, ES6ML master

Updates us to the lastest of both.
Makes @loader work with es6

This updates to the latest steal, systemjs, and es6-module-loader with
fixes for running es6 modules with multiple loaders loading at the same
time.
Add test for transpiling CommonJS modules

This was broken in <= 0.4.0, CommonJS modules after being transpiled
would export an object that included the module value's including
`exports`. This is fixed by the SystemJS upgrade. Just adding the test
to verify it doesn't happen again. Fixes #85
Fix contributing guide link.

Closes #90.
Merge pull request #91 from bitovi/fix-contributing-link

Fix contributing guide link.
pointing to latest steal
Merge pull request #87 from bitovi/cjs-exports

Add test for transpiling CommonJS modules
Fix resloving traceurRuntime path on windows

Fix for correct resloving traceurRuntime path also on windows
Merge pull request #98 from whitecolor/patch-4

Fix for traceur path resolution on windows
Use the latest Steal minor branch

This upgrades us to the latest Steal minor branch which had a couple of bug fixes that shouldn't cause any problems.
Merge pull request #106 from bitovi/latest-minor

Use the latest Steal minor branch
Upgrade to latest transpile

This updates us to use the latest transpile from the minor branch.
Merge pull request #107 from bitovi/latest-transpile

Upgrade to latest transpile
Reset window.define before evaling in pluginify

Our System.define shim needs to have the same logic as our AMD shim.
That is, before executing code remove our `window.define` and replace it
with the original version, and then set back to our version after the
eval. This causes problems with "bad AMD". That is AMD that has it's
define statement at the bottom and therefore must be marked as a global.
Fixes #73
Merge pull request #108 from bitovi/system-eval

Reset window.define before evaling in pluginify
Show file size of bundles in verbose mode

If verbose mode is enabled, output the file size as part of writing out
the bundles. Fixes #56
Merge pull request #109 from bitovi/bundle-sizes

Show file size of bundles in verbose mode
Only include Traceur runtime if used

This changes, based on the new version of Traceur, to only include the
runtime if the source is using the runtime. Because the runtime no
longer uses the `assertObject` calls it used to, for simple scenarios
such as only importing/exporting the runtime is not needed. This changes
`has_es6` to instead of testing the format, test for the presence of
`$traceurRuntime` in the source. Fixes #75 and #99