When processing index.js files, use the parent directory name.

Many 'require' implementations map 'index.js' files to their parent directory name when mapping script files to module names. Examples include Node.js and Webpack (http://webpack.github.io/). If there is demand, this could be made configurable. I think Dojo defaults this to 'main.js', but most people use 'index.js' these days.

When processing 'require' call expressions, this patch maps ".." to the parent directory (unchanged). With this patch applied, the Closure Compiler resolves modules relative to the entry file the same way Node.js and Webpack do.