Mimic ssh(1) behaviour with host key prompt

Resolves #50

ssh-askpass

@@ -33,9 +33,14 @@ on run argv
             display dialog args with icon agent default button {get localized string of "OK"} default answer ""
         end if
         return result's text returned
-    else if args contains "host" then
-            display dialog args with icon agent buttons {"No", "Yes"}
-            return result's text
+    else if args contains " host " then
+        display dialog args with icon agent default button 1 cancel button 2 buttons {"OK", "No", "Yes"} default answer ""
+        set host_key_result to result
+        if text returned of host_key_result is not "" then
+            return text returned of host_key_result
+        else
+            return button returned of host_key_result
+        end if
     else
         display dialog args with icon agent default button 1 giving up after dialog_timeout
         if gave up of result then