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_while.wren

@@ -0,0 +1,9 @@
+var f
+while (true) {
+  var i = "i"
+  f = fn IO.print(i)
+  break
+}
+
+f.call
+// expect: i