fix. abort method does not attempt reset to a start tag when one does not exist.

Change-Id: I975b03bdba582d80318eafa9c3a36dcbc7ae3a34
fix. dulwich tagging.

Change-Id: I49a10a52b68e81db3c8c1569d70fab563c99004a
fix. remove debugger statement + pep8.

Change-Id: Ib02124bc23d6e5df85ada06c34800e4fd2e79cac