Hello,

Triggered by a bug report in Debian where a (TeX) virtual font was
mis-detected as MS-DOS executable, I took a brief glance into the story
and realized things are bad: All these files usually just have 16 bits
of magic which is way too weak.

To improve things at least a bit:

For dvi, there is a "command byte" after the preamble. By probing for
that we can increase the magic to at least 24 bit. Also, we have
pstrings now - this avoids some garbage in the output (that very command
byte usually).

For vf, there is a command byte as well, acceptable values are 243
through 245, however I've only encountered 243 in some 20k examples.

Those who want to dig further, or want to improve the other two file
formats, check the texlive-bin package, program sources are:

    TeX packed font data:   texk/ps2pk/pkin.c
    TeX generic font data:  texk/dvipsk/loadfont.c
    TeX virtual font data:  texk/dvipsk/virtualfont.c
    TeX DVI file:           texk/dvipsk/prescan.c

Look for "!=247", this is the check for the first octet.

Cheers,

    Christoph
