Fix build failures with --disable-shadowgrp. Thanks to Jürgen

Daubert for the patch.
* libmisc/salt.c: Include <stdio.h>, needed for stderr and printf
  functions.
* lib/encrypt.c: Include <stdio.h>, needed for perror, stderr and
  printf functions
* src/usermod.c: sgr_locked exists only if SHADOWGRP is defined.
* src/chgpasswd.c: Only check is the gshadow file exists if
  SHADOWGRP is defined.

lib/encrypt.c

@@ -32,8 +32,11 @@
 #ident "$Id$"
 
 #include <unistd.h>
+#include <stdio.h>
+
 #include "prototypes.h"
 #include "defines.h"
+
 char *pw_encrypt (const char *clear, const char *salt)
 {
 	static char cipher[128];

lib/groupio.c

@@ -3,6 +3,8 @@
 
 #ident "$Id$"
 
+#include <stdio.h>
+
 #include "prototypes.h"
 #include "defines.h"
 #include "commonio.h"
@@ -230,7 +232,7 @@ static int group_open_hook (void)
  * same name, password and gid.
  *
  * It merge the members of the second entry in the first one, and return
- * the modified first entry on success, or NUll on failure (with errno
+ * the modified first entry on success, or NULL on failure (with errno
  * set).
  */
 static struct commonio_entry *merge_group_entries (struct commonio_entry *gr1,