Add build.xml.dist to XML filenames

Ant uses `build.xml` for it's configuration, but [many projects](https://github.com/search?utf8=%E2%9C%93&q=filename%3Abuild.xml.dist+project&type=Code&ref=searchresults) including my own commit a `build.xml.dist` file and ignore a `build.xml` file, allowing for a custom configuration if necessary.

I've added `build.xml.dist` to the `languages.yml` file to enable syntax highlighting on GitHub for `build.xml.dist` files.