don't truncate 100 char long paths in tar extraction

When a data.tar.{gz,xz} contains a path name that is exactly
100 characters long, it will get truncated to 99 chars upon
extraction in ExtractTar::Go().

Using all of the 100 available characters for the filename
seems to be new behaviour in gnu tar.

Closes: #689582
Thanks: Mika Eloranta for the testcase!
add a testcase for 100 char long path truncate bug #689582

Git-Dch: Ignore