test-dont-use-too-old-dep.py: fix tarfile timestamps

test-dont-use-too-old-dep.py: fix tarfile timestamps

It turns out that TarFile.addfile() doesn't provide a reasonable default
timestamp, resulting in files dated to 1970 (they're probably wearing
bell-bottoms and listening to disco too). Then, when the bdist_egg command
tries to create a *zip*file with those files, it explodes because zipfiles
cannot handle timestamps before 1980 (it prefers boomboxes and jackets with
straps on the shoulders, thank you very much).

This puts a modern time.time() on the members of the tarfile, allowing future
cryptocoderarchaeologists the opportunity to make fun of fashion trends from
the user's chosen era, rather than an artificially older one.

refs #1342