MinGW win32 console with TERM set to xterm

[Mike Gran]

Hi-

I was trying out the MinGW ncurses snapshot from a
a couple of weeks ago, trying to get the Guile binding
of ncurses to run on MinGW.

The Guile binding's test suite sets TERM=xterm, so
that the results are consistent regardless of the terminal
on which the test suite is running.  So I noticed that
for #w32con, some ncurses functions ignore the TERM
variable and give the #w32con value instead.

For example, with TERM=xterm, the procedures use_default_colors,
assume_default_colors and the term_attrs have different values
on MinGW vs other systems.

(But in the real world, no one would try to use TERM=xterm
on MinGW after they've compiled in TERM_DRIVER, so I can't
say if it is worth modifying.)

Thanks,
Mike Gran