use .gist instead of prefix:<~> to stringify REPL autoprint output

Now when the return value of an expression is a type object, you get Int()
or so, and no warning

src/Perl6/Compiler.nqp

@@ -16,6 +16,16 @@ class Perl6::Compiler is HLL::Compiler {
         %*COMPILING<%?OPTIONS> := %options;
         $super(self, |@args, |%options);
     }
+
+    method autoprint($value) {
+        unless pir::getinterp__P().stdout_handle().tell() > $*AUTOPRINTPOS {
+            if pir::can($value, 'gist') {
+                nqp::say(nqp::unbox_s($value.gist));
+            } else {
+                nqp::say(~$value);
+            }
+        }
+    }
 }