Don't remove environment variables such as PATH or SHELL.

http://bugs.gentoo.org/show_bug.cgi?id=301957
https://alioth.debian.org/scm/browser.php?group_id=30580

--- a/src/su.c
+++ b/src/su.c
@@ -342,7 +342,7 @@
 #endif
 #endif				/* !USE_PAM */
 
-	sanitize_env ();
+	/* sanitize_env (); */
 
 	(void) setlocale (LC_ALL, "");
 	(void) bindtextdomain (PACKAGE, LOCALEDIR);