Added three commands: delete-empty-revs, list-large-files, and add-git-ignore

delete-empty revisions will delete empty revisions in a svn dump file.
list-large-files will list the largest files.  The number listed is an
   option to the command
add-git-ignore creates a new dump file that adds a .gitignore file that
   contains the contents of the svn:ignore property for those directories
   that have the svn:ignore property set.