Add Support-Map Tests for Rhino

This patch adds Support Map Tests to the rhino test suite.  It makes the following changes:

1. Add compiled version of source-map (version 0.1.31) because Rhino can't dynamically pull in dependencies
2. Add source-map to the Rhino build with a Header/Footer that wraps source-map as a less-friendly dependency
3. Add hooks in RhinoTest to support per-test bootstraping and validation
4. Add a SourceMapRhinoTest that bootstraps SourceMap tests and then validates them after they run
5. Update lib/less/rhino.js to properly handle (some) source-map options and add a new one (--source-map-output-map-file) that will output the source-map to a separate file (so we can validate our Rhino tests)
6. Add a new testRhinoSourceMap and add it to the test list

Also makes some minor bug fixes:
A.  Fix typo in the Gruntfile.js for the sourcemap-test
B.  Update Gradle build to always build the less-rhino-<version>.js before running the tests
C. Remove unused callback in less-test.js