[Mtools] Security bug: Path traversal due to "/" in file names.

[Timothy Baldwin]

There is no check for "/" in filenames, so extracting files from a specially
crafted filesystem will result if files outside the target directory being
written.

For example, extracting from this image:
http://www.majoroak.f2s.com/tim/linux/dosfs-exploit.gz

With:
mkdir test
mcopy -sv -i image ::TEST test/

Results in following extra directories:
test/TEST2
test/TEST3
T

-- 
OpenPGP key fingerprint: D0A6 F403 9745 CED4 6B3B  94CC 8D74 8FC9 9F7F CFE4