shadow-4.0.11 breaks shadow group support

Hi

This latest release breaks shadow group suport. For example, trying to run
grpconv results in:

$ grpconv
grpconv: not configured for shadow group support.

This worked fine in shadow-4.0.10

It seems the cause is related to the definition of `SHADOWGRP' ie: it longer
gets defined.

--------------------------------------
>From configure script of shadow-4.0.10

if test "$enable_shadowgrp" != "no"; then
        cat >>confdefs.h <<\_ACEOF
#define SHADOWGRP 1
_ACEOF

fi
--------------------------------------
>From configure script of shadow-4.0.11

if test "$enable_shadowgrp" = "yes"; then

cat >>confdefs.h <<\_ACEOF
#define SHADOWGRP 1
_ACEOF

fi
--------------------------------------

It appears `enable_shadowgrp' is not defined anywhere so in actual fact,
this has been broken all along and only worked in the last release by
chance.

Additionally, there is a separate autoconf check for shadow group support
but it defines something else (HAVE_SHADOWGRP) but this check appears to be
broken anyway because it always fails:

  checking for working shadow group support... no

config.log shows this:

configure:22999: checking for working shadow group support
configure:23025: gcc -o conftest -O2 -pipe  -s conftest.c  >&5
conftest.c: In function `main':
conftest.c:99: warning: initialization makes pointer from integer without a cast
conftest.c:101: error: dereferencing pointer to incomplete type
conftest.c:101: error: dereferencing pointer to incomplete type
configure:23028: $? = 1
configure: program exited with status 1
configure: failed program was:



In summary, it appears shadow group support is very broken and the
autoconfigury is confused. I'm not sure of the best way to fix it.

Regards
Greg