Eliminate use of setpwent()/endpwent() and setgrent()/endgrent().

Sudo never iterates over the passwd or group file.
Rename sudo_set{pw,gr}ent() -> sudo_mk{pw,gr}cache() and
use sudo_free{pw,gr}cache() instead of sudo_end{pw,gr}ent().

plugins/sudoers/logging.c

@@ -623,9 +623,7 @@ send_mail(const char *fmt, ...)
 
     sudoers_setlocale(SUDOERS_LOCALE_SUDOERS, NULL);
 
-    /* Close password, group and other fds so we don't leak. */
-    sudo_endpwent();
-    sudo_endgrent();
+    /* Close fds so we don't leak anything. */
     closefrom(STDERR_FILENO + 1);
 
     if (pipe(pfd) == -1) {