EOF character changing

[Jim Reuter]

The reason System V (and System III and System whatever-else-Bell-sells)
changes the EOF character is because of the raw-mode delays
they added. When in raw mode in v7, every character coming
in wakes up the process reading the line, which can swamp
a system.  System III and friends in raw mode have both a
minimum-character threshold and a time threshold before waking up
the reading process, the intent being a reduction of system load. 
Unfortunately, they decided to multiplex the character-count and
time thresholds into already existing variables, namely the EOF and
the BRK (I think) character.  So, the ioctl code automatically sets
these fields to the 'appropriate' values when switching between raw
and cooked mode (ICANON mode for those systems).  Assuming, of
course, that you consider their canned values 'appropriate'.

Don't hold me to the constant and variable names mentioned above,
I don't have the stuff in front of me and it has been a while.

	Jim