lib/agetpass.h: Move prototypes to dedicated header

Signed-off-by: Alejandro Colomar <alx@kernel.org>

src/gpasswd.c

@@ -20,6 +20,7 @@
 #include <stdio.h>
 #include <sys/types.h>
 
+#include "agetpass.h"
 #include "alloc.h"
 #include "defines.h"
 #include "groupio.h"

src/newgrp.c

@@ -17,6 +17,7 @@
 #include <stdio.h>
 #include <assert.h>
 
+#include "agetpass.h"
 #include "alloc.h"
 #include "defines.h"
 #include "getdef.h"

src/passwd.c

@@ -20,6 +20,7 @@
 #include <sys/types.h>
 #include <time.h>
 
+#include "agetpass.h"
 #include "alloc.h"
 #include "defines.h"
 #include "getdef.h"

src/sulogin.c

@@ -16,6 +16,8 @@
 #include <signal.h>
 #include <stdio.h>
 #include <sys/ioctl.h>
+
+#include "agetpass.h"
 #include "defines.h"
 #include "getdef.h"
 #include "memzero.h"