ant requires hg to be installed; convert this code to use git instead

The ant build files that all of the projects in this repo use require hg to be installed. However, since the repo is now versioned with git, hg is not necessary. In fact, the build file with utilities used by all of the projects, ant-util.xml, should be re-written to use git to extract the version id (which is what the hg command was used for originally).