the check for 'bs'... my previous commit should have included the
following text:
fixes problem introduced in 1.13 where the setting of "BC" (backspace char)
was left to libterm rather than being done by hack itself. the problem
with this was that hack was directly setting BC to \b if there was no
"bc" in the termcap entry, but libterm does not do this. this resulted in
the xputs(BC) calls in nocmov() and backsp() incorrectly doing nothing, thus
messing up the display. added new var BC_BS to provide the old behavior
for nocmov() and backsp().
