DPB accumulates changelog instead of adding recent changes only

In case of option 'Check out to sub-directory' is on, the plugin gathers all of the changes ever made plus recent changes and pushes it back to git repository instead of extracting recent changes only, even if it was not the first commit.

If not to use sub-directories in github plugin everything works as expected.

Start by reproducing the issue with the Jenkins plugin's “Check out to sub-directory” option enabled, then inspect the code that extracts and pushes changelog changes. Compare behavior after the first commit with the configuration disabled; done means only changes since the previous build are pushed when sub-directories are used.

Written by the indexing model from the issue text.