I forgot that chpass(1) and passwd(1) reach-around into libc for

I forgot that chpass(1) and passwd(1) reach-around into libc for
getpwent.c (isn't it horrible), and therefore lack visibility of
the the libc-internal __hash_open() function.  Use -DFORCE_DBOPEN
in chpass/Makefile and passwd/Makefile and adjust getpwent.c to
use the external visible interface.  Is there a better way?