[tlbuild] Buffer overrun in dvi2tty

[Ken Brown]

Here's another matter to be dealt with after the freeze is over: The 
function getfname in dvi2tty.c has no checks to prevent buffer overruns. 
  I discovered this when dvi2tty.test was mysteriously failing when I 
built TL in a directory with long path names.

As a side note, the value of 100 for MAXLEN in dvi2tty.c seems 
unnecessarily small.

Ken