When investigating issue #4859 I found that when pwd.getpwall()
and grp.getgrall() fail due to decoding errors, they leave open
file descriptors referring to the passwd and group files, since
they don't call the end*ent() functions in this case.  Also, the
grp.* functions have a reference counting error when they fail in
this way - a debug build reports that an object's reference count
goes to -1.  What I think happens is that in mkgrent(),
PyStructSequence_SET_ITEM steals the reference to "w", meaning
that the "Py_DECREF(w)" call shouldn't be made afterwards.  The
attached diff fixes both of these problems, I think, and applies
to the 2.x and 3.x branches.