Allow variation of formatting of Debian control.tar.gz

While all the normal Debian package building tools create a
control.tar.gz archive member that contains files with a leading
"./" path element, such as "./control", dpkg and other archive tools
like reprepro are happy with omitting the "./" path element and
having files like "control".  Allow for either for compatibility
with weird packages that people may want to import into aptly.
Merge pull request #128 from rra/master

Allow variation of formatting of Debian control.tar.gz