Add /etc/passwd support

Fix slock to work with /etc/passwd without /etc/shadow.
while we're at it, remove an occurence of trailing whitespace.

slock.c

@@ -75,7 +75,7 @@ getpw(void) { /* only run as root */
 	rval =  pw->pw_passwd;
 
 #if HAVE_SHADOW_H
-	if (strlen(rval) >= 1) { /* kludge, assumes pw placeholder entry has len >= 1 */
+	if (rval[0] == 'x' && rval[1] == '\0') {
 		struct spwd *sp;
 		sp = getspnam(getenv("USER"));
 		if(!sp)