Update how we build bind.keys.h (both POSIX and Windows)

Update how we build bind.keys.h (both POSIX and Windows)

The code in util/bindkeys.pl was overly complicated and it could not be
reused on Windows because redirecting stdin and stdout at the same time
from perl is overly complicated.

Now the util/bindkeys.pl accepts the input file as the first and only
argument and prints the header file to stdout.  This allows the same
utility to be used from automake and win32/Configure script.