Fix scoping and break statements.

Variables declared in the loop were not properly disposed of
when you broke out of the loop.

test/break/closure_in_for.wren

@@ -0,0 +1,9 @@
+var f
+for (i in [1, 2, 3]) {
+  var j = 4
+  f = fn IO.print(i + j)
+  break
+}
+
+f.call
+// expect: 5