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

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

test/break/exit_local_scopes.wren

@@ -0,0 +1,18 @@
+for (i in 0..10) {
+  IO.print(i)
+
+  {
+    var a = "a"
+    {
+      var b = "b"
+      {
+        var c = "c"
+        if (i > 1) break
+      }
+    }
+  }
+}
+
+// expect: 0
+// expect: 1
+// expect: 2

test/break/nested_for_loop.wren

@@ -0,0 +1,19 @@
+for (i in 0..2) {
+  IO.print("outer " + i.toString)
+  if (i > 1) break
+
+  for (j in 0..2) {
+    IO.print("inner " + j.toString)
+    if (j > 1) break
+  }
+}
+
+// expect: outer 0
+// expect: inner 0
+// expect: inner 1
+// expect: inner 2
+// expect: outer 1
+// expect: inner 0
+// expect: inner 1
+// expect: inner 2
+// expect: outer 2