several fixes from bad copy+paste. Add in a test for 'can' override

src/pmc/object.pmc

@@ -645,7 +645,7 @@ non-zero value if it does.
 
         if (!PMC_IS_NULL(method)) {
             INTVAL result = 0;
-            Parrot_ext_call(INTERP, method, "PiS->I", SELF, &result);
+            Parrot_ext_call(INTERP, method, "PiS->I", SELF, method_name, &result);
             return result;
         }
         else {
@@ -681,7 +681,7 @@ Returns whether the object's class is or inherits from C<*classname>.
 
         if (!PMC_IS_NULL(method)) {
             INTVAL result = 0;
-            Parrot_ext_call(INTERP, method, "PiP->I", SELF, &result);
+            Parrot_ext_call(INTERP, method, "PiP->I", SELF, lookup, &result);
             return result;
         }
 
@@ -711,7 +711,7 @@ Returns whether the class is or inherits from C<*classname>.
 
         if (!PMC_IS_NULL(method)) {
             INTVAL result = 0;
-            Parrot_ext_call(INTERP, method, "PiS->I", SELF, &result);
+            Parrot_ext_call(INTERP, method, "PiS->I", SELF, classname, &result);
             return result;
         }
         else if (SELF->vtable->whoami == classname

t/pmc/object-meths.t

@@ -5,7 +5,7 @@ use strict;
 use warnings;
 use lib qw( . lib ../lib ../../lib );
 use Test::More;
-use Parrot::Test tests => 37;
+use Parrot::Test tests => 38;
 
 =head1 NAME
 
@@ -1121,6 +1121,26 @@ CODE
 /Method 'new' not found for non-object/
 OUTPUT
 
+pir_output_is( <<'CODE', <<'OUTPUT', "overloading can vtable" );
+.namespace [ 'Foo' ]
+
+.sub 'can' :vtable("can") :method
+    .param string role
+    .return(1)
+.end
+
+.namespace []
+
+.sub main :main
+    $P0 = newclass "Foo"
+    $P1 = new $P0
+    $I0 = can $P1, "no_method_i_ever_heard_of"
+    say $I0
+.end
+CODE
+1
+OUTPUT
+
 # Local Variables:
 #   mode: cperl
 #   cperl-indent-level: 4