Build fix on Mac OS X.

Legacy Java 6 for Mac OS X has tools.jar, but now we use Java 7 or above
version.  so there is need to add tools.jar on Mac OS X.
Merge pull request #138 from noraesae/plugin-test

Add task to test plugin JavaScript APIs.
Add ScriptableHttpClient.

ScriptableHttpClient is the module to send HTTP request from the Beyond
plugin. It refers to Node's SuperAgent package for its API design.

The test case is added as plugins/test/http-client.js