Use $SUDO_ASKPASS if defined. Allows non-terminal sudo password prompts.

The sudo program checks this env var and uses it, but only if --askpass
was given at the command line, or if it thinks there is no terminal.
But the terminal detection is unreliable, so give it --askpass if there
is an askpass program defined in the environment.

To try it, simply "export SUDO_ASKPASS=/usr/bin/ssh-askpass" before
running tomb.

For me personally, this makes it possible to have a hotkey to run
"pass" and "pass tomb" related commands.  Without this patch, invoking
via hotkey causes my window manager to lock up while waiting for a
password on the VT where Xorg was started... and since it's locked up,
I can't change to the VT to enter the data it's waiting for.  So I have
to log in via ssh from another host to recover it.

So, instead of locking up... now it can use a GUI askpass program.

tomb

@@ -136,7 +136,8 @@ _sudo() {
 		local msg="[sudo] Enter password for user ::1 user:: to gain superuser privileges"
 		command -v gettext 1>/dev/null 2>/dev/null && msg="$(gettext -s "$msg")"
 		msg=${(S)msg//::1*::/$USER}
-		sudo -p "
+		[[ -n "$SUDO_ASKPASS" ]] && local sudo_askpass="--askpass"
+		sudo $sudo_askpass -p "
 $msg
 
 " ${@}