The Cygwin-w32 currently supports battery status via the function 
w32fns.c:Fw32_battery_status.  The X11 and nox builds don't have this 
support, and Cygwin lacks the facilities used on unix-like systems to 
provide it (/proc/apm, etc.).  But it turns out to be easy to compile 
and use Fw32_battery_status on all Cygwin builds, simply by pulling it 
out of w32fns.c into a new file.

The attached patch does this.  OK to push?  If so, to which branch?

Ken