When creating tar archives using the tarfile module, requested arc names
are not respected. 

It is currently impossible to create a tar which when listing contents
would give:
$tar tvf test.tar
./
./control
./prerm
./postinst

The actual result will be
$tar tvf test.tar
./
control
prerm
postinst

This is caused by TarInfo's tobuf method calling normpath() on all file
names, even when the user has explicitly specified a certain name.