Add Support Map Tests

This patch adds Support Map Tests to the rhino test suite.  It makes the
following changes:

1.  Fix typo in the Gruntfile.js for the sourcemap-test
2.  Update Gradle build to always build the less-rhino-<version>.js
before running the tests
3. Add a new testRhinoSourceMap and add it to the test list
4. Add a SourceMapRhinoTest that bootstraps SourceMap tests and then
validates them after they run
5. Add hooks in RhinoTest to support custom bootstraping and validation
6. Add compiled version of source-map (version 0.1.31) because Rhino
can't dynamically pull in dependencies
7. Add source-map to the Rhino build with a Header/Footer that wraps
source-map as a less-friendly dependency
8. 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)
9. Remove unused callback in less-test.js
Merge pull request #13 from dhaber/rhino-source-map-tests

Add Support-Map Tests for Rhino