XXX: the reverse mapping case (last subsubtest in t_basic) does
not make any sense, but apparently that how umapfs works. I'm not
familiar enough with the code to determine if this is a wanted
feature or a pure and simple bug.
This change converts all the existing regression tests in
regress/sys/fs/tmpfs to the new framework provided by atf. As a side
effect, this also moves all the tests programs in regress/sys/fs/tmpfs to
tests/fs/tmpfs.