add put*ent functions for passwd/group files and similar for shadow

since shadow does not yet support enumeration (getspent), the
corresponding FILE-based get and put versions are also subbed out for
now. this is partly out of laziness and partly because it's not clear
how they should work in the presence of TCB shadow files. the stubs
should make it possible to compile some software that expects them to
exist, but such software still may not work properly.

include/grp.h

@@ -36,6 +36,7 @@ void           setgrent(void);
 
 #ifdef _GNU_SOURCE
 struct group  *fgetgrent(FILE *stream);
+int putgrent(const struct group *, FILE *);
 #endif
 
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)

include/pwd.h

@@ -39,6 +39,7 @@ int getpwnam_r (const char *, struct passwd *, char *, size_t, struct passwd **)
 
 #ifdef _GNU_SOURCE
 struct passwd *fgetpwent(FILE *);
+int putpwent(const struct passwd *, FILE *);
 #endif
 
 #ifdef __cplusplus

src/passwd/fgetspent.c

+#include "pwf.h"
+
+struct spwd *fgetspent(FILE *f)
+{
+	return 0;
+}
+
+int putspent(const struct spwd *sp, FILE *f)
+{
+	return -1;
+}

src/passwd/putgrent.c

+#include <grp.h>
+#include <stdio.h>
+
+int putgrent(const struct group *gr, FILE *f)
+{
+	int r;
+	size_t i;
+	flockfile(f);
+	r = fprintf(f, "%s:%s:%d:", gr->gr_name, gr->gr_passwd, gr->gr_gid);
+	if (gr->gr_mem) for (i=0; gr->gr_mem[i]; i++)
+		if (fprintf(f, "%s%s", i?",":"", gr->gr_mem[i])<0) r = -1;
+	funlockfile(f);
+	return r<0 ? -1 : 0;
+}

src/passwd/putpwent.c

+#include <pwd.h>
+#include <stdio.h>
+
+int putpwent(const struct passwd *pw, FILE *f)
+{
+	return fprintf(f, "%s:%s:%d:%d:%s:%s:%s\n",
+		pw->pw_name, pw->pw_passwd, pw->pw_uid, pw->pw_gid,
+		pw->pw_gecos, pw->pw_dir, pw->pw_shell)<0 ? -1 : 0;
+}