chg: do not close dir fd while iterating
It works so long as the dp is the last entry, but readdir(dp) would fail
with EBADF. Let's not do that and close the dir fd explicitly.
chg: show debug message for each fd to be closed
It helps debugging. The number of file descriptors should be small in most
cases, so the console output wouldn't get bloated even with CHG_DEBUG=1.