github PR #891 - tty #if HANGUPHANDLING misspelled

Pull request from entrez:  the conditional hangup handling in
wintty.c hasn't been getting used because the HANGUPHANDLING macro
from the core was misspelled as HANGUP_HANDLING.

The old testing was probably invalid since it was most likely done
with the same misspelled #if.  I haven't done any new testing so
since this should be considered potentially buggy.

Fixes #891