Currently, on checkout the plugin gets the HEAD. However, that's not always what you want. In our case, the pipeline is triggered on each check-in, with the changeset being passed as a parameter. Since there is a lag between the time the trigger from check-in is fired to the the time were the build starts, there is a race condition were other changes might come in. 

It would be beneficial to haven an optional parameter to checkout to sync to a defined changeset. The default wold be to sync to HEAD.