Make smartmatching Iterables against Lists use same semantics as Arrays

S03-smartmatch/array-array.t tests smartmatching against Lists.
TimToady++ suggests adding some pattern type for smart matching against
lists. However, we're trying to get to the same functional level as nom
now. We can always create new semantics later.

Makes array-array.t pass.

src/core/List.pm

@@ -378,7 +378,37 @@ my class List does Iterable does Positional { # declared in BOOTSTRAP
         }.new(self)
     }
 
-    multi method ACCEPTS(List:D: $topic) { self }
+    multi method ACCEPTS(List:D: $topic) {
+        return ?self unless nqp::istype($topic, Iterable);
+        my $sseq = self;
+        my $tseq = $topic;
+
+        my int $spos = 0;
+        my int $tpos = 0;
+        while $spos < +$sseq {
+            # if the next element is Whatever
+            if nqp::istype($sseq[$spos], Whatever) {
+                # skip over all of the Whatevers
+                $spos = $spos + 1
+                    while $spos <= +$sseq && nqp::istype($sseq[$spos], Whatever);
+                # if nothing left, we're done
+                return True if !($spos < +$sseq);
+                # find a target matching our new target
+                $tpos = $tpos + 1
+                    while ($tpos < +$tseq) && $tseq[$tpos] !== $sseq[$spos];
+                # return false if we ran out
+                return False if !($tpos < +$tseq);
+            }
+            elsif $tpos >= +$tseq || $tseq[$tpos] !=== $sseq[$spos] {
+                return False;
+            }
+            # skip matching elements
+            $spos = $spos + 1;
+            $tpos = $tpos + 1;
+        }
+        # If nothing left to match, we're successful.
+        $tpos >= +$tseq;
+    }
 
     multi method list(List:D:) { self }