Added -S flag (read passwd from stdin) and tgetpass_flags global

that holds flags to be passed in to tgetpass().  Change echo_off
param to tgetpass() into a flags field.  There are currently 2
possible flags for tgetpass(): TGP_ECHO and TGP_STDIN.  In tgetpass(),
abstract the echo set/clear via macros and if (flags & TGP_ECHO)
but echo is not set on the terminal, but sure to set it.

auth/sudo_auth.c

@@ -155,7 +155,8 @@ verify_user(prompt)
 #ifdef AUTH_STANDALONE
 	p = prompt;
 #else
-	p = (char *) tgetpass(prompt, def_ival(I_PW_TIMEOUT) * 60, 1);
+	p = (char *) tgetpass(prompt, def_ival(I_PW_TIMEOUT) * 60,
+	    tgetpass_flags);
 	if (!p || *p == '\0')
 	    nil_pw = 1;
 #endif /* AUTH_STANDALONE */