Accept the value of $SHELL or the shell in the user's password entry,
even if it's not found in /etc/shells.

Patch by Mark H Weaver <mhw@netris.org>.

--- xterm/main.c.orig	2014-01-15 21:12:25.000000000 -0500
+++ xterm/main.c	2014-02-13 01:55:04.840576171 -0500
@@ -4570,12 +4570,12 @@
 	    if (validShell(explicit_shname)) {
 		xtermSetenv("SHELL", explicit_shname);
 		shell_path = explicit_shname;
-	    } else if (validShell(shell_path = x_getenv("SHELL"))) {
+	    } else if (shell_path = x_getenv("SHELL")) {
 		;		/* OK */
 	    } else if ((!OkPasswd(&pw) && !x_getpwuid(screen->uid, &pw))
 		       || *(shell_path = x_strdup(pw.pw_shell)) == 0) {
 		shell_path = resetShell(shell_path);
-	    } else if (validShell(shell_path)) {
+	    } else if (x_nonempty(shell_path)) {
 		xtermSetenv("SHELL", shell_path);
 	    } else {
 		shell_path = resetShell(shell_path);