M3 is recognized as Logitech

[stsp]

As pointed here:
dosemu2/dosemu2#974 (comment)
ctmouse treats "M3" as logitech and therefore
doesn't work in dosemu2 w/o the patch that changes
to "M". According to this document:
https://github.com/joyent/sdcboot/blob/master/freedos/doc/ctmouse/protocol.txt
it is an expected behaviour. But that document was
written by ctmouse authors, and may therefore be
biased.
I have the following evidences of the opposite:

• None of many other mouse drivers I tried, were convinced
  by "M3" to use logitech protocol.
• There is another document:
  http://webcache.googleusercontent.com/search?q=cache:Koa5jJW4QCsJ:www.klick-im-unglueck.de/TP/serial.htm+&cd=4&hl=ru&ct=clnk&gl=ru
  saying:

Three-button-mice sends 'M3' if you
drop and raise RTS (see above) in Microsoft mode; this is compatible
with the Microsoft mouse driver and allows the firmware to check if it
is really a three-button mouse.
                   [Scott David Daniels received this info from Brian Onn]

I fear that by obeying to the ctmouse impl I broke
the middle button support.